Exhaust manifolds used on most classic American car engines are cast-iron, which can cause problems after long use because it is brittle and can break or warp. A warped manifold can often be salvaged by having it resurfaced in the same manner as a cylinder head. However, when a mounting ear or a flange corner breaks off, your best alternative is to purchase a new manifold or find a good used one. Recently, some aftermarket manufacturers have begun producing some of the more popular replacement manifolds, but the less common units are often only available from used parts sources. Many makes with similar engine sizes shared a common exhaust manifold in classic cars, which makes finding an acceptable substitute at a local salvage yard relatively easy. You should pay attention to year ranges, as many early engines did not have A.I.R. emissions or thermactor pumps. Body styles are important because of where the exhaust system connects; some cars do not have enough clearance inside the engine compartment to fit around shock towers, power steering or control arms. The dimensions of the exhaust ports also vary. Listed here are some of the makes and models that are likely candidates for a used manifold to fit your car. Unless otherwise stated, these interchanges pertain to full-size cars and light trucks.
Buick: 1964-'66 401 and 425 use the same passenger manifold; 1962-'64 401 and 425 use the same driver's side manifold; 1969-'75 400/430/455; 1968-'74 350 passenger manifold; 1968-'70 350 driver's side; 1971-'74 350 driver's side
Cadillac: 1958-'65 365/390/429 en-gines have the same driver's side manifold; 1968-'75 472/500 except Eldorado use the same left manifold; 1968-'69 and 1975-'76 472/500 uses the same right manifold
Chevrolet: 1940-'48 6-cylinder; 1949-'53 216 engines use the same manifold; 1950-'62 cars and trucks w/235 and downdraft carburetor will fit; 1963-'74 cars and trucks (except 292) 6-cylinder manifolds are the same; 1955-'56 V-8 manifolds with A/C are the same, but check exhaust pipe diameter; 1957-'70 283/307/327 passenger manifolds are the same; 1957-'63 283 driver's side manifolds interchange; 1967-'70 396/454 Camaro, Nova and Chevelle manifolds are the same; 1965-'68 283/307/327 left side will fit non-A.I.R. cars and A/T trucks; 1969-'75 327/350/400 left side can be used in earlier years if A.I.R. holes are plugged; 1969-'79 307//327/350/400 pass. car and 1969-'87 trucks right side are the same; 1967-'78 396/454 without A.I.R. passenger side manifolds interchange; 1973-'97 454 truck left manifolds with A.I.R. and O2 holes; 1985-'97 454 truck right manifolds are the same; 1973-'82 passenger side manifolds in car and trucks are the same.
Chrysler: 1954-'59 6-cylinder manifolds interchange; 1960-'68 6-cylinder manifolds can be exchanged; 1970-'86 225 6-cylinder will interchange; 1956-'59 277/318 both manifolds will substitute within these years; 1964-'73 273/318 right manifolds interchange; 1965-'68 273/318 (except Dart, Barracuda) left manifolds interchange; 1978-'80 318 passenger manifold is the same as for trucks; 1969-'70 340 passenger side all, left side fits Dart, Valiant until 1973; 1968-'69 383 Dart and Barracuda both manifolds interchange.
Dodge Trucks: 1965-'69 273/318 manifolds will interchange; 1978-'85 318/360 and 400 can be exchanged; 1972-'78 440 manifolds will interchange.
Ford/Mercury: 1960-'66 170/200 6-cylinder passenger cars and 1961-'64 Econoline; 1967-'72 170/200 6-cylinder including 1966-'74 Bronco; 1960 Edsel and 1958-'62 Ford 352/390; 1955-'62 Ford 272/292/312 with dual exhaust; 1963-'73 260/289/302 right manifolds also in 1970-'76 Maverick; 1963-'73 260/289/302 left manifolds except Galaxie, Full-size and Maverick; 1963-'67 352/390 in Galaxie and Thunderbird; 1969-'73 351W interchange in Mustang, Galaxie and Fairlane; 1966-'69 390/428 manifolds in Galaxie and Thunderbird; 1968-'73 429 and 1970-'80 460 manifolds are the same; 1975-'82 351M/400 engines, both car and truck are interchangeable.
Obviously, these are not all the exhaust manifold interchanges that are possible. Other manifolds will fit with adaptations to the exhaust or the addition of accessory brackets that may be missing from an earlier year manifold.