Poly A-block 318 Parts Interchange

(many parts applicable to 277, 301, 303, 313, and 326)

I have compiled this list of poly 318 parts interchange (along with other A-blocks) with notes to assist in piecing together A-blocks. I use the A-block years 1956 – 1966 understanding that 1966 parts were used through 1967 in some export cars/trucks. For parts numbers and recommendations, see the complete A-block parts list.

Blocks:

  • 1956 – 1961 A-block
    • Note: Bellhousing bolt/alignment pattern, starter location, water jackets differ from later A-blocks.
  • 1962 – 1966 A-block

Camshaft: All A-block

  • Note: LA camshaft do not interchange.

Connecting Rods: All A303/313/318 and all LA with floating pins

Connecting Rod Bearings: All A/LA

Crankshafts:

  • 1956 – 1961 depending on stroke
  • 1962 onward A/LA except LA360 and externally balanced cast-crank LA340

Cylinder heads:

  • 1956 – 1961 A-block
    • Note: 1956 – 1960 heads do not have accessory bosses drilled/tapped.
    • Note: 1962 – 1966 heads can be used on 1957 – 1961 but not the other way around because 1956 – 1961 heads have additional coolant passages that dump coolant into the lifter valley on 1962 – 1966 blocks.
  • 1962 – 1966 A-block

Distributor: All A/LA

Distributor Drive Gear: All A/LA

Exhaust Manifolds: All A-block

  • Exhaust manifolds can be used on either right or left heads.
  • A-block cars often came with one center-dump and one rear outlet.
  • A-block trucks often came with two center-dump.
  • Generator right manifolds had a generator bracket incorporated.

Flywheel/Flexplate:

  • 1956 – 1961 A-block 
  • 1962 onward A/LA except externally balanced LA360/LA340
  • Note: LA360 and cast-crank LA340 flexplates/flywheels can either be neutral balanced or weighted to balance the rotating assembly. Using them requires verifying neutral balance.

Fuel Pump: All A/LA

Fuel Pump Eccentric: All A/LA

Harmonic Damper: All A and internally balanced LA

  • Note: When using an LA damper with an A-block timing cover, see the notes under “Timing Cover” below and my page on harmonic dampers for more details on interchanging dampers and timing covers.
  • Note: LA360 and cast-crank LA340 do not use dampers but balancers and will throw the A-block rotating assembly out of balance. See my page on harmonic dampers for more details.

Intake Manifold: All A-block

Lifters: All A-block

  • Note: LA lifters will fit but are taller than A lifters and require shorter pushrods.

Main Bearings: All A/LA except LA360, which have larger journals

Oil Filter and Housing:

Oil pan:

  • 1956 – 1961 A-block
  • 1962 onward A/LA except LA360, due to the larger journals.
    • Note: Trucks used a front-sump pan, cars a center-sump pan. Car pans will not clear the factory truck suspension (Figures 2 and 3).

Oil pump:

  • 1956 – 1961 A-block
  • 1962 onward A/LA

Pistons: All A318

Piston Rings: A/LA with 3.91″ bore

Pulleys:

  • Crank: All A/LA
  • Water Pump: All A/LA
  • 1957 – 1969 pumps have a short shaft and require a pulley to match.
  • 1970 onward pumps have a long shaft and require a pulley to match.

Pushrods: 

  • Solid Lifters: All solid-lifter A-block
  • Hydraulic Lifters: All hydraulic-lifter A-block
    • Note: LA pushrods do not interchange.

Rocker Arms: 1956 – 1966 A-block

  • Note: LA rocker arms do not interchange.

Rocker Arm Shafts: 1956 – 1966 A-block

  • Note: LA rocker arm shafts do not interchange.

Starter Motor: 

  • 1956 – 1961 auto and manual transmission: A-block or manual LA
  • 1962 – 1966 manual transmission: A-block or manual LA
  • 1962 – 1966 auto transmission: A/LA/Magnum
    • Note: For headers/tight clearance, use either the 1993 onward Magnum min-starter or aftermarket high-torque mini-starter.

Timing Chain Set: All A/LA

Timing Cover:

  • 1956 is unique
  • 1957 onward A/LA except 360, due to the larger journals
    • 1957 – 1961 timing covers are iron. 1962 onward are aluminum.
    • LA273/318/340 timing covers will physically bolt onto an A-block, but they lack one bolt hole on the left side. In the A-block, this boss goes through into a water jacket. To use the LA timing cover on an A-block, plug the block hole using a set screw or cutoff bolt and proper sealant (such as Permatex 80003) prior to installing the timing-cover gasket.
    • If using an A-block damper with the TDC clocked on the right with a 1970 onward LA timing cover with the molded timing pointer on the left, remark the damper TDC line with a file or timing tape with cylinder 1 at true TDC. If using a 1970 onward LA damper with a 1970 onward LA timing cover, the markers align. See my page on harmonic dampers for more details on interchanging dampers and timing covers.

Thermostat: All A/LA

Thermostat Housing: All A/LA and first-generation hemi-blocks

Valve Covers: All A-block

  • 1956 – 1958 and some 1959 have three bolt holes but will interchange with all year A-blocks (see Figure 1 below).
  • All A-block heads have the center bolt hole boss drilled and tapped through end of production in 1966.

Valve Springs: All A/LA

  • Note: Follow camshaft spring-rate requirements
  • Note: Verify spring height works with aftermarket valves.

Valve Spring Retainers: All A/LA

Valve Spring Keepers: All A/LA

  • Some valves have double grooves and some triple. Match keepers to the valves.

Water Pump: 

  • 1956 is unique
  • 1957 onward A/LA
    • Use 1957 – 1969 short-shaft pump for left-side intake.
    • Use 1970 onward long-shaft pump for right-side intake.
    • The water pump pulley must match the pump style (short or long) for belt alignment.
Figures

Mopar A-block poly valve covers
Figure 1: Valve Covers (photo by J. Lotspeich)
Mopar A-block poly car oil pan
Figure 2 – Car Oil Pan (photo by J. Lotspeich)
Mopar A-block poly truck oil pan
Figure 3 – Truck Oil Pan (photo by J. Lotspeich)