manifold removal - stuck on oversize stud

[Zetomagneto]

I once lapped a warped head on my landlord's plate glass mirror, the head was serviceable after but the mirror wasn't!

Nowadays I lap on an old iron surface plate (eBay) which is not perfect but near as makes no difference. I lay a sheet of abrasive paper on top of it (grit up!) and give it a good squirt of WD40 for lubrication. That way the surface plate stays flat. For larger parts I have used abrasive paper from a floor sander. Keep rotating the part and the imperfections should even out. Not as flat as milling but a useful tool for a light clean-up.

Quick skim at your recondioners then you know its flat