Hi cosullivan there are many different ways to remove paint one of the best ways would be to sandblast,but you wouldn't do the engine that way.Like most people (me included) don't have a sandblaster.So then to get get somebody to do then cost money.Maybe more than it would be worth.
So you need to find the best way for you to do it.Like for what I can see most the paint still seems to be in reasonable condition.So for that I would just use somewhere from 100grit to 400grit sandpaper just to scuff the surface,giving the new paint something to stick to.Or if you wanted to go deeper you could use paint stripper,however that can get messy.For the steel parts I use a Technic called electrolysis,it's brilliant will remove all the paint and even rust.It will only work with steel no alloy.For your case I'd just use sandpaper no setting up and no real mess at the end,may take a little longer.For the engine and head I'd just use a wire bush on a drill.As I said you'd have to work out what is best for you.
I hope that helps.
