[427TJ]

If you were going to have a Motion (427 or 454) car built and were going to order it new through Baldwin Chev, then Motion (Joel Rosen) preferred you to order an L78 car. That way, the car came with HD running gear (hi-perf speedos and tachs too) and the factory L78 could be sold over the parts counter at Baldwin. Baldwin likely gave the buyer a credit for giving back the L78.

But, if you were on a budget and could not afford to begin with an L78 car then Motion would happily work on and convert just about anything. Logically, Motion wanted the most able platform to begin an upgrade on (an L78 car) but they probably did 427/454 swaps on everything from Z/28s to six-cylinder cars.

Good to point out that JoeG's Phase III Chevelle began life as an L78 and kept the L78 for the Phase conversion. Again, if you didn't have the bucks (or desire) to go for the full 427/454 conversion then you could have your 396 massaged to Phase I, II, or III specifications.