Yes the manifolds will swap, the only issues you may run into is accessory pulleys. They changed the belt spacing on the 68 & 69 250 engines. So if the 68 engine does not come with pulleys, or if your car has power steering and the 68 car does not and only has a single groove water pump pulley, you can't use your 67 2 groove water pump pulley as the belts will not be straight and you will throw the power steering belt at higher rpms. I have made most of those mistakes in the past when swapping parts between engines over the years.
Also you will notice a big loss in HP using the 1bb engine. Even if you swap the manifolds & cam.
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Jeff R
60 Jaguar Mark 2, 3.8L Automatic
67 Sprint Firebird 230 OHC-6 4-Speed A/C
78 Catlina Safari, Pontiac 400 powered
77 Astre Formula, 215 Buick V-8 T-5
73 Lemans Safari, 400 4bbl 4-speed
71 Catalina Enforcer, 455 4bbl
06 Mallet Solstice #024 LS2, Now with a Tremec 6060 6-speed!
2012 F-150 Echo Boost (My local Ford Dealer SUX!!!)
2020 Dodge Charger Scat pack (recovered)
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