Here is a I O Sonic I raced against back around 1988 in APBA A class, it rocked.

Coool! Single or twin?

Twin stock 300 hp small blocks Chevy's running at 70+ speeds.

Thats impressive. Would have liked to have seen that.
I like the idea of the small blocks in the smaller boats. It would be fun to build a couple of the all aluminum small blocks and drop in.
I think you could probably get what, 500 reliable HP's per??

I heard they raced some O/B's too but never seen any pix's have you?

500 would be easy, and some really nice motors

When I worked at Performer in the early 90's we built the same boat, one of them we built "Special" to beat Reggie in the Rudee Run, a 200 mile race from Hopewell Va to Va Beach & Back. The boat we built had twin "Staggered" 540's and #4 drives on boxes. it ran 114 mph with the tabs down, if you lifted the tabs it would start porpoising and jumping out of the water (On Glassy river water) at 90-100 mph it would jump a 100'+ (distance, Not hight) repeatedly until you put the tabs down. Fun Times

When you really need to make a heavy boat go fast, big blocks are your friend

24'

that might be a fun project in an old school 30' Velocity which is on my short list for that 30' I/O boat. Wouldn't have the mid range torque that big blocks would and not sure how that would equate at a 3500 RPM cruising speed but every where else I'd think you'd have a winner.
I think they set a record back in the day w/small blocks into the 80's.

Here are a few O/B from back in the day..