What paint for diff?

Well, for 1] herculiner is a coating, not a paint.

Are you thinking of painting and then undercoating?

Or just undercoating?

Not sure where U are in restoration, but seems some metal priming?

Right (and right on the priming), however all those steps are interlinked. I'm not media-blasting the parts until I know what paint I want to use, which will also drive the choice of primer.

POR-15 is good for rust protection, but it really requires a blasted finish. If you want a more "resto" look, you can topcoat POR-15 with "chassis black" before it fully dries.

nate

You don't need to use the same primer on the body as on the underside. I do like the Locktite stuff personally, then followed by a sticky bituminized coating. The better coatings have some reducing agent added to slow rust down, but it's more important that the coating be covering everything and in all the nooks and crannies than that it be anything fancy.

--scott