455?!? Taking the big blocks out now huh? LOL. I had one of the last 302s in a 95, but had it bored .40 and stroked 1/2". After everything was said and done, only thing left from the old engine was the block. Mind you, I'm not getting 25 mph by any means but with the stock gear I still get 15-16 mph around 70 and 12-13 mph at 55.
Yep, its a low compression '73 motor, but I worked the stock heads (J castings) till they flowed better than C or F heads on the exhaust side. Running stock size valves with a 268* duration/450* lift camshaft. Still stock bore/stroke. Also using HEI distributor for hotter igniton so I don't have to run it so rich, have maximum advance set to about 34*, and it runs perfectly fine on regular unleaded, no detonation whatsoever.
Because it is a big block, its in-town mileage is not so satisfactory, but thats a reasonable trade-off for me.