[RKDinOKC]

Back in the day had a Full Size 81 GMC Jimmy. It had a 305 that was anemic. Bought and old 78 Monte Carlo with the big valve 400 and swapped em out. Had to take the Jimmy to an inspection place and for $5 the guy checked the serial number off the engine block and gave me an emissions exemption certificate. Pre 1980 vehicles were exempt from emissions. So since the motor was from a pre-1980 was able to run the 81 without smog stuff including catalytic converter. Went from 12 to 20 mpg to boot.

So can understand the logic of putting in an older powerplant.