Any crate engine, IMO, needs to be torn down and at least inspected. The only way they can make any $ on these at the prices they sell them, is to do mass production, and buy parts in bulk. Bulk parts vary in quality from very good to just passing, and sometimes unusable. Mass production is just that, and leaves many opportunities for mistakes. I know there are plenty of successful installations of these engines, but there are enough horror stories that IMO, it's not worth taking the chance. Clearances need checking, machine finishes, cranks, rods, balance, heads, guides, etc. all need to be at least verified for correct. If anyone knows about these engines and the parts that go into them it's Chris, and he's right. Even if the guide clearances are set correctly, the valves are el cheapo. Likewise with the springs. Bore to piston clearances are most likely too tight for marine use (hot piston cold block syndrome) and I've heard the bearing clearances are tight, as well. The biggest complaint I've heard with these engines are oil pressure complaints. An oil pan upgrade should be in order as well. Re-assembled corectly, these should be good engines and give plenty of reliable service.
JMO
One more thing to add: If you're targeting a specific power requirement, it might be beneficial to flow the heads and get a specific cam ground. especially in a jet boat. NO doubt you'll be leaving power on the table if you don't. You're also compromising a lot of the potential of any engine you run with that ex system (that I see in your pics) Might consider an ex upgrade to compliment your engine upgrade.