With the engine back from the machine shop, I've started with assembly of the head. My original plan is to use the 1.5 rocker with the standard pressed steel rockers as a backup if required (I think these are 1.3?). The 266SS cam gives .270" of lift so the total lift depending on the rockers;
1.5 rockers
270 x 1.5 - 12 (tappet clearance) = 0.393" = 9.98mm
1.3 rockers
270 x 1.3 - 12 = 0.339" = 8.61mm
With the 12G295 head machined with hardened valve seats, I checked the installed spring height to be 1.280". Tighter than what I was expecting, I wanted to make sure that I wasn't going to bind the springs with these high lift rockers. I set the head up in the drill press to make it easy to compress the valve and set up the dial gauge.
This photo shows the high lift of the 1.5 rockers. We are a bee's peen away from binding with these AEA526 springs, but there should be a little more clearance with the AEA525 springs that I plan to use - so sweet, no spring crush.
What I didn't realize when compressing the spring to the near 10mm valve lift was that the valve spring cap had completely crushed the valve stem seal and punched out the center of it.
After this, I wanted to check to see if the lower lift of the 1.3 rockers saw the valve spring cap foul the valve stem seal.
It is a little difficult to see in this photo, but the cap is just touching the valve stem seal by about 0.15mm - definitely not something I am happy to live with. I measured up the valve guide and they're currently sitting 15.00mm proud of the valve spring seat. I think I could get away with gently driving all of the valve guides down to about 14mm.
Another option I am considering is machining about 1.5mm off the inside bottom edge of the valve spring cap. In the above photo, the collets are installed and seated as far down as they go. There looks to be about nearly 3mm of clearance between the bottom edge of the cap and the collets, so I think I could machine off about 1.5mm from these edges to get the relief I need without affecting the seating of the collets.
From all that I've read, with the 12G295 head, there probably is no need to go to the highest lift of the 1.5 rockers but making both adjustments of deepening the valve guides and machining the valve spring cap a smidge, I will have the option to run both.
While I consider what to do and where to find/buy a lathe, I started on assembling the rods and pistons. Strangely one of the piston rings for the pistons was 0.1mm wider than all the others and wouldn't fit any of the pistons! A quick call to GR and a new set are on their way. Thanks Graham!