A little more progress. Pictured is the extension shaft, which mounts on the original countershaft, and is carried in an outboard pillow block. The pillow block base will bolt to a "cage" that mounts to the main crankcases and original motor mount pickup points. The idea is to keep location of the shaft "dead true" regardless of engine fit-up (such as removing for tech inspection...just in case it ever gets fast enough). The extension shaft coupler uses part of the original shock damper, and is pilot bored to fit over the original output shaft nipple.
The extension shaft has a 48mm outer, on the coupler, to allow for a crankcase seal. The seal will be carried in a bolt-on cup, to allow centering on the shaft before locking down the seal. It's also important to have the seal floating free while alignment of the shaft is confirmed. This is the same method used to put front main seals on old Land Cruisers (install pulley with timing cover bolts loose, then bolt down cover).
I also included a shot of the reworked left side of the frame, to allow for the new chain-run orientation. I have enough clearance to carry a 17T countershaft sprocket (the biggest available for CB500T).
Regards, JimL