I originally purchased my Procomp 210's new from a well know head supplier in Ohio. My heads had 2 issues that I had to repair. First the pushrod holes were not aligned with the rockers, thus requiring drilling out the holes and sleeving them with ultra thin brass to prevent oil from entering the intake ports. To get better rocker alignment after this repair, I used Isky adjustable guide plates to get decent alignment.
The second issue is also well documented in that the valve guides wear quickly. Even though I had the rockers aligned as mentioned above, 2 valve guides had excessive wear within 1000 miles. Under warranty, my head supplier sent me 3 guides to fix the problem (they would have done it themselves, but I have free access to machinist equipment and wanted to save the shipping costs.) Come to find out that the guides used were not even a commonly available part here in the USA. Had to turn down the ones sent to get the correct outer diameter.
After all the work and new stainless valves, the isky guide plates, the brass sleeves, I had $1100 (no labor charges) in a pair of Procomps. My heads worked fine for a couple of years, with the only other issue being that valve cover gaskets would not last very long as the heads sealing ridge did not fully match the valve cover gaskets and stock valve covers on the intake side of the heads. I tried rubber, cork, doubled cork and all were temporary fixes.
Here is my pair with the new valves, ARP rocker studs, and .700 lift springs, less the Isky guide plates:
I later traded some stuff for a pair of used AFR 210's and can't say enough about them. I could tell the difference on the street in 3rd gear in all RPM ranges (not counting the increased high speed potential in 4th) and I gained 7mph at the track with little more a swap of $1300 used heads. Other quality heads can be purchased new in the $1400 range.
That is my ACTUAL experience, which mirrors many reports on the web.
Aside from the problems that I experienced, I have also heard from trusted individuals on Yellow Bullet about valve seats dropping out of position and ruining good engines. Are you feeling lucky?
Good Luck with your project, however you choose to proceed.