Tim. Most of the engine and other detail parts are made of white metal. I have a three step method of prepping and painting them
1. removing seams, drilling appropriate holes and sanding any unwanted cast marks.
2. I put the parts in small batches into a magnetic tumbler with a burnishing fluid for about 15- 20 minutes for cleaning and polishing.
3. Prime , base coat, color. I use mostly Alclad for my metal colors. But I do leave the parts polished if it calls for it. Like the air boxes. I used 1500 grit sand paper then 3000 grit, then I polished it with rubbing compound . Then shot some 2k clear to seal the decals.