Can an A500 be 100% converted yto A500+ ?

[zipper]

Yes. You need KS 2.x, 0.5 MB trapdoor expansion (or chip addition onto the mobo on later revisions), Denise 8373, Megachip 2 or equivalent and mobo jumper work, depending on the revision. Just what I've done years ago.

[zipper]

Here's a description, photo and even instructions for mobo modifications:
http://amiga.resource.cx/exp/megachip