1984 26' Bertram convertible

I'm assuming you are stating you have the old straight 6 cylinder Chevy blocks and asking if Small block v-8 would work? Also assuming inboard vs, stern drive. If your stern drive you have to stay with the slim blocks.
IMO, the ole 6s produce more torque than a 305 v-8. 350 v-8 matches the torque and exceeds the hp. If you have the room (sure you do on I/B design) it would work.
However, support on those ole 6s will be around still for a long time.

So, the old questions. What's wrong with what you have? OR, do you just want to go faster and consume more fuel?

Hi-tech v-8s look cool. Mostly reliable. Those 6's were a work horse and hard to kill.
Now, invest in a pair of diesels (will fit) and you have an investment that will pay near and at resale.

Well then, all you need is another 5 inches forward. I think same mounting pads.
How 'bout the diesel idea?

It's a boat. Trouble was built in at the factory.
However newer diesels are not that much heaver but will cost allot more, Maybe not 30k each but allot more. NYCAPT makes a good point also about resale comparables and must be considered with other questions; Is this a high hour boat? You gonna keep her a while or flip her soon. There are some more questions and money balances if your thinking short/long/hours/resale/keeper/ yada, yada.

Yep new V-6s or 8s could be fun, fast and cheaper, but keep your options open if your high hour or a keeper.

AND, Keep us up on what you decide with progress reports. We all learn here.