Well I'll throw a little sand in the Vaseline for this powdercoat love in
I agree powdercoat is the best but paint works fine too, I was in a panic once and used Tremclad directly on sandblasted tin, that was 10+ years ago and it still looks new today. The bus gets driven daily, even in the rain, but I do avoid salt. Carb cleaner and other solvents don't hurt it either. I did use the stuff in the can and put it on with a gun, the spraybomb stuff sucks.
Whatever you decide do a trial fit on all the tin first, type 4 tin gets mangled, it sticks out the sides of the engine and gets bashed when the engines out and often gets bent when someone attempts to remove a piece without dropping the engine, it also sometimes warps during blasting and even gets stepped on by the blaster occasionally. You don't want any gaps to leak air and powdercoat sometimes cracks when you straighten a piece after coating, get it all dialed in first.