I just got a call from the cylinder head shop. They said that the installed spring height on the intake side is 1.550; it should be 1.750 for my springs, and, unless I'm mistaken, the stock installed height should be 1.780. Thinking that the problem could be the overall length of the replacement valves (5.078), they tried an off-the-shelf valve with overall length of 5.090 (same as stock) with the same result. The intake seats, as far as I know, are original, are within specs, and reusable. Other than taking the original valves that were removed from the heads to the shop and having them recheck the installed height, I don't know what to do. Is there a plausible explanation for the installed being short by .200?

Hi, .200 long SBC  valves should help.

Non-stock retainers and the addition of spring cups/spring seats comes to mind for taking away the available spring height requirement.  Valve locks are also a player as they are available in ~+/- 0.050” increments beyond stock.  I just did a set of stock 239 EBU-F heads with the 5.090” long valves and those heads had 1.825” between the retainers and the cylinder head before adding the springs.  That left plenty of room to shim the valve springs for the desired pressure.

Lorena, Texas (South of Waco)

Another thought on the subject.

It's not mentioned if or what machine work was performed on the guide bosses to accommodate non-stock Y valve springs.  A conventional height mic does not fit all the way down to the bottom of valve spring seat area of the head on the stock Y heads.  If the shop doing the heads is not watching for this, the measurement will come up short if using a height mic.  For stock Y heads, I will typically use a ‘snap gauge’ and a specially adapted dial caliper in lieu of a height mic for valve spring height measurements.

Lorena, Texas (South of Waco)

I'll keep this info. handy when I return to the machine shop. I wouldn't have thought of it, unless I saw the spring height being measured, but a machinist should be able to see it and know.