"Family" swaps are Period correct

I've talked before about "Period Correct" modifications, but I had a conversation with a guy yesterday that got me thinking, and I felt compelled to write this. He asked me to look at a hot rod he was thinking about buying. The car was a 1964 Pontiac Tempest. It had a killer 425 inch Olds motor built by Mondello Performance ( Joe Mondello is THE Olds Guru, like Smokey Yunick with Chevys or Dick Landy with Mopars ) a B&M Turbo 400, and a 9 inch Ford rearend with 4.30 gears. It had big-n-little ( 14X6 front, 15X8.5 rear ) American Racing Torq-thrusts, and a gorgeous black paint job. And the guy selling it had timeslips from his local strip showing that the car ran a best time of 11.88 at 121 mph! The car had "badass" written all over it. If I didn't already have too many cars, I would have bought it. The buyer was apprehensive over the Olds powertrain. I told him-"Hey, it's a Tempest, not a GTO, so who cares?" "And, that's the beauty of GM cars, everything interchanges." "And people did this all the time in the '60's and '70's." "Motion Performance and Baldwin Chevrolet, that built L88 427 and LS6 454 Canaros in the early '70s offered the same conversion to Firebird owners." "High Performance cars even road tested an LS6 Firebird in 1972, and raved about how cool it was." "I've seen countless Firebirds, Cutlasses, and LeMans's with big-block Chevys in them." "I've even seen a Buick Skylark and a Chevy El Camino, both with a 455 Pontiac engine under the hood."  "If you want this car, buy it." "I mean, if the emblems on the fender said "Cutlass" instead of "Tempest" you'd be jumping up and down over your great find." "Ditto if had a 421 Pontiac under the hood instead of a 425 Olds." "GM has always done this." "How many Olds Omegas, and Pontiac Venturas had Chevy engines in them from the factory?"  "Thousands of Pontiac Firebirds from 1977-79 had 350 Chevy or 403 Olds engines from the factory."  So if you find a great deal on a GM car and it's been "Cross-breeded" don't panic. I probably wouldn't buy a 69 Judge with a Rat motor in it, but a 68 Tempest, hell yeah, if it was done right. Something to think about. Mastermind