What would you recommend for a scratch with some surface rust?

[Suberman]

I think you maybe overthinking this small job mate, just leave the Epoxy to go hard, key i and apply topcoat.

I'm starting to think so too. Frankly i'm really thinking that a regular primer will do, which in this case, i'm going to just use the 1K etch wash primer that i was given and then a coat of paint over that.

I'd have slapped a couple of brushfuls of Zinc 182 or used the Dinitrol spray straight on it and then painted it when it dried, half an hour tops in the temperatures you are talking there. Is it some kind of exotic supercar or expensive vintage motor ?

Unforutantely it is not, but i still want to get it done well and learn the as i go along.