I think your firewall looks pretty darn good, so if it were me I’d clean it up with a Scotch pad and steel wool and leave it as is. You made a good decision not to repaint the truck, as I like originality. I happen to think that those trucks at the car shows that have been shot with clear look wrong. What’s right about shiny rust?!? If you’re going to drop in a shiny brand new motor, either a rebuilt six or an SBC, then I’d dress up the engine bay, otherwise leave it alone. It matches the exterior. Remember, it’s only original once.
