I am curious which would be the better choice. I would like to build around a 650 HP engine for a single engine boat. Would I be better off with a blower motor with low boost or a naturally aspirated engine? What would be the pros and cons? Any input would be greatly appreciated. Thanks!

What kind of cubic inch you thinking. 454-502 sc 540 up na. You really should look at Dennis r 565 in the swap. You can't build solid reliable HP for that kind of money.

I agree buy the 565 Dennis has for sale. Way ahead $ wise.
If all you want is 650 HP build a 540 with 10 to 1 compression and AFR aluminum heads and it will make your HP goal and run on midgrade fuel.

Another option is to build a mild supercharged 540ci motor to get to your 650HP goal and then throw more boost at it when 650HP is not quite enough.