Well Done!
Thanks for this excellent contribution to the forum! I followed everything you had said and it all makes perfect sence. I had also heard that aftermarket companies were selling replacement Diamond precups, but they were very inexpensive. Once used in GM heads, they would protrude .002" out of the hole, on a set of heads that had proper depth for a precup (tools are available to reset). So to use them would mean increasing the depth of the precup hole to accept the aftermarket (and probably inferior) precup.
I really like how you group the heads side-by-side, you can plainly see differences externally on the heads on BOTH the intake side and the exhaust side.
I'm also disappointed that they are being difficult with the return.
Back a few years ago I purchased as set of heads from Alabama Cylinder heads. I was advised by Benny Avant (Diesel Depot) that the heads were inferior and that if I could that it would be best to send them back. Alabama Cylinder Heads did take the heads back, with a no-questions asked attitude, even paid the shipping back to them, and refunded the entire costs that I spent on them. I didn't even get to argue, I was out absolutly nothing.
So, it seems that you've found out that the Clearwater heads are no better than the Alabama Cylinder heads. There are differences between the two, I think there are three variants of these aftermarket heads in circulation.
1982 C10 SCSWB 6.5TD, mods too extensive to list. (13.69 1/4 mile @94.6 MPH) RACE TRUCK
1982 C10 SCSWB 6.2NA, 2.73 700
1986 C10 SCLWB 6.2TD 3.73 700
1989 V20 SUB 6.2NA, 3.73 400
1994 G20 VAN 6.5NA, 3.42 60E
1994 K20LD ECSWB 6.5TD, 3.42 80E
1995 K20 SUB 6.5TD, Wrecked, ran into by stupid teen.
1995 C3500HD DRW 6.5TD, 12' Flatbed 5.13 80E
1995 C3500HD DRW 6.5TD, 18' Rollback Wrecker 4.63 80E
1994 C20HD ECLWB 6.5TD 3.73 80E Wifes Truck.
1995 C20LD ECSWB 6.5TD 3.73 80E
1995 K20LD SCLWB 6.5TD 3.73 80E
1996 K30 DRW 6.5TD 4.10 80E
1997 C10 Tahoe 2Door 2WD 5.7L to 6.5 Conversion Underway