Yes it'll be fine. I've even used it on air cooled engines without it blistering or peeling in the past, and they get much hotter than most marine engines.
Try a car paint and panel factors or industrial paint outlet and ask for plant paint. This is uasually a very tolerant polyeurathane paint at reasonable cost and is designed for industrial pumps, pipework etc in a wide range of standard colours. They will be able to closely match original colour also. Raw water direct cooled engines run very cool, so temp wouldn't be an issue, & prob also OK with indirect cooling.
Bit late with this, been painting!!
try www.frost.co.uk the do really good engine enamel.
Alsorts of other stuff, not the cheapest but all tried and tested.
nice mini, i found a paint called hard hat, wich seams to be very good, heat and oil tollerant with a supurb finish. available in spray cans from paint and decorators suppliers.
I toyed with the idea of de-seaming and even a chop, but went down the original route.
But I made it far too fast for road use. When I built it I used to live in the East Riding where you can get a move on, but here it's a nightmare. Stone walls, narrow lanes, slow tourists and standing traffic. I don't have weekends to myself now so the plan to hillclimb and sprint hit the rocks. So I sold it. Lost £2000. I spent £6000 on bits for it.
The paint is cellulose applied by my fair hand. The motor was built up by Mike Barrett of Lincoln. Ace engine man (he also does 16 valve heads and injection (which he makes) for minis).
It had over 125 BHP and did the 60 dash in under 7 seconds. However I never got it quite spot on, although the Pirellis look lovely, they are crap on grip.
Sold it to a guy in Anglesy who was going to sprint it he said.