An L20 isn't a direct bolt it.

So that wouldn't be too easy. But it is still possible.

I fI were you I would wait until the majorty of the work is done before painting it.

If you need to lips guards or modify other bits it woudl be annoying tohave to do it again. Or if you accidently scratch the paint gettign the old engine out.

Try out martins Datsun page for some basics:
To Start you Off

Umm oh yeah where are you? What country etc...