What would be the basid difference in 454 vs 502 ? I am assuming newer Generation 454 EFI ....

bigger cylinder bore, bigger pistons to match, another 35-40 hp.

no major difference in Block design ?

yep .....mag ...the question arose when because member "upthecreek" is looking for a boat and several he is looking at are similar boats but some have the 454 and some 502 ..prob the year of boat I guess ...

Go with a 502 boat cause you can stroke them to 540'S. More torque is better.