I believe that when the tool was revised to make the 1/24 '70 TA, a new and better engine was on the punch list. I have all the Monogram 2nd gens and will give a look to see what's what in the engine department.

IMO the best Pontiac engine so far is the '66 GTO engine from Revell. Only option is a tri-power intake, but that can be remedied with a parts box swap. Honorable mention to the JL '64 GTO engine, which is also very accurate, scaled from a correct reference point; for any pre-66 build (upcoming '65 GTO, for example) it is a good choice.