I remember seeing a '68 Biscayne post for sale back around the late 70's around the Hamilton, Ontario, Canada area. It was black but painted white underneath and had ladder bars that looked like barn trusses that extended forward to what seemed to be in line with the front of the rear seat base. It had skinny Cragars up front & steam roller Cragars out back, plus a hood scoop that was a dead ringer for a Hemi Dart. Of course it was a built 427 4-speed with impractical gearing out back.
Back then one used to see for sale a lot of thrashed street cars or some tasty strip cars based on factory musclecars. Numbers-matching was nice but few gave a care and just ran whatever they had. Finding a freshly wrecked musclecar with a hopped-up power-train to donate whatever was salvageable was no problem. I'm sure thousands of Impalas donated 427s.

Oh, to go back in time with cash, a connected dealer & an order sheet. I envision a '69 Biscayne with an L-72, M22 and an MA6 Dual-Disk Clutch (which would delay and ultimately mean modifying or canceling the order, but one can dream). Or Baldwin-Motion could set you up (or Central Chev-Olds in London or Gorries in Toronto, or any of the dozens of speed shops around any given city back then).