I ve got a pair of 454 Mags 1992 model they have retangler port heads by ser# and Carbs thinking about going to 502 is there that much difference between the two. What do yall think stay the same and rebuild or buy 502 long blocks?

If you are doing full rebuilds, stroke your 454's by changing the cranks and pistons and make them 496's.

If you current engines dont need full rebuilds, you can do a cam swap, intake, carb, and exhaust to wake them up. You can make about 450HP with the 454, rect port heads, and proper cam.

If you need cranks, pistons, etc, than it would be worth it to do the stroker kit to go to 489+CI. But if all your bottom end is intact, i'd spend the money on stuff for the top end.

Another idea, is if your bottom ends are toast, and you need to start from scratch, you can pretty much get a new 540 shortblock complete for not much more than it will cost to piece together a 496 stroker or 502. Then you are getting a new stronger better built block. Your heads can work on a 540 if money is tight, and make 550-575HP and lots of torque.