What to tell the machine shop

If it was only that easy.....

Can you explain what level of performance you are looking for?
If you are just looking for a small performance upgrade, you do not need bigger valves, porting, oversized push rods, etc. Just a set of Rock Auto 340 replacement springs and you will be good to go. You could even shave your head 50-100 thousands and have clearance on a stock 225. You should have adjustment clearance with stock push rods.
If you are looking for the 13's or faster you will need a serious game plan.
Have you talked with Oregon Cams? They have quite a few slant grinds that have worked well and they can regrind your cam and lifters also. That might be the answer for your machine shop on how to set up the head.
Plan twice, spend once!