318 diagnosis

Bore scope is a good start.
Just the valves being different heights scares me about the head work done. I’d be pulling the heads and start there.
Look for knurled guides and worn valves. Valve heights off can cause a bunch of issues. Does it have valve seals?

When a good machine shop does the work you know it and pay for it. Not sure where you got stuff done or bought from but a fresh engine typically does not burn oil just because.
Good luck and keep us posted.