The engine rebuild is moving along: the cylinder head is still at the machine shop, and the block has joined it there, but we may not continue with the same block.
I knew that the block had previous issues with a dropped thrust washer; the rear washer had dropped before i started working on the car, and after taking it apart it was obvious that it had also happened at least once before. The thrust washer is a known weak point of these engines, because it only covers 180° of the crank face, and is prone to accelerated wear if the clutch is pushed in when the engine is started.
On my engine, it's apparent that it's happened before because the rear main bearing cap (the one that takes the brunt of the lateral force if the thrust washer drops) had been repaired at some point by welding a new steel face on the damaged rear surface. This is a questionable repair because it tends to warp the cap, and there was still damage on the opposing bearing face of the crank, which prevented a good bearing interface there. In short, it was a short-term fix and it's no surprise that it failed again.
The machinist said that it's fixable, but would cost about $500 to fix the cap properly and another $500 for a line bore, and that's on top of any other work that's needed. He recommended finding a new block, or at least a new rear cap.
Enter TR6 block #2. Happily, the local Triumph club came through again and i was connected with an early short block that had been sitting outside for a while, but was pretty cheap and intact, including the same long crank that mine has. It was not turning, and i was warned that the pistons would need to be broken out, but i was able to get the pistons, lifters, and cam put without breaking anything.
There's some rust in various pockets, including on the crank journals, but aside from the rust the crank is in better shape than mine, so i'm hopeful that maybe i could use both the block and crank and save the extra repair time on mine. I'm planning to get this block fully stripped and cleaned up and bring it to the engine shop for evaluation later this week.