I know nothing about your boat, will it handle 80mph or just become dangerous

I agre with all that replacing motor with low hour from forum is the least expensive and best way to go, that been said, i opted to restore boat, make it a real pretty solid boat first replacing what was needed and upgrading everything replaced with an eyt to performance., you need to have your boat ready **before** you add big hp and speed.
That is why the previous poster asked about steering.
My pre motor replacement will include: Proper gauges, full hydrolic steering, k-planes, performance outdrive (mine alpha) bolster then a real motor. Several 540's have passed the classified section lately 550-650 hp under $8k then sell 454 to offset cost.
Again situations and need for speed, to finish varies amoung us all.
Lots of luck. Look foward good to follow progress.

Stock Power steering, which also will be upgraded.

Probably become slighty dangerous

Be ready to replace that Alpha if going into the hp your talking about. Will it run with an Alpha? Sure, but not long.

I have a Bravo one drive

Keep in mind that even the Bravo 1 is vulnerable to HP levels above 500. Especially the early model Bravo's, even more so with a lot of hours on them. If you plan to romp on it, plan on going through it and possibly upgrading it for more strength, or find yourself a spare to have sitting at the ready for when it goes kapow next summer with 650 HP running through it.

Might want to add a new coupler to that list as well. See what I mean about that slippery financial slope that is high performance boating? It will drive you to drinking.