BBC is pretty universal as far as hopping up.
Not much if anything changes internally between the
Merc version and the others.
Drive is the only thing that changes.
What hp is it rated?
Is it carbed or fuel injected?
What year?
Also just try doing a search on here using 454 as a keyword on this forum
http://www.***boat.com/forums/forumd...to_forumsearch
I loved the Formulas especially the older ones.
I wanted to buy another one when I found my current boat and the deal was just too good to pass up. (Im poor )
I have had a 21LS with a 350/Alpha and a 17 F1 with a 140 Johnson, my cousin has had the famous 233 Openfisherman with twin 225hp outboards , a 233 longdeck with twin 350 Mercs, and currently an F18 with a 350 merc . One thing you want to check is the straighness of the bottom in the rear. In the mid 80s Formula put a lot of hook in their bottoms, dont know if that applies to your 91 but its worth a check,,if it has it just grinding it out and smoothing the bottom will get you 4-5mph on the top end easlily.