273 update
Build a 360 shortblock, and install all the 273- 2bbl finish parts, but with bigger exhaust parts. Then paint it 273 Red, and re-install the 273 pie-plate on it.
Very few people will know the difference, until you give them a ride.
I did this in about 1975 , with a 340 short and a 318 top including heads and cam; into a 65 Valiant wagon. She was a terror in two gears. And the 318 cam made her a drive it anywhere/anytime DD.