I had figured out in my head that I would use some rose joints and an adjustable link bar as the upper mount. The link bar would allow me to shorten or lengthen mount which would effectively raise or lower the diff thus adjusting the tension of the chain.
As pictured here I welded a nut between the two inserts. The theory being I could use a spanner to turn the link bar once fitted to the car however, this made the overall length of the link too long so I later ground the welds down and welded the two inserts together. I might make another one later with a slightly better design.
rear sprocket alignment & mounting
I grabbed a piece of wood and clamped it to the front sprocket. I then supported and clamped the rear sprocket to it also so I could tack the cradle rose joint tab to the cradle.
Everything lined up well and the rose joint has some adjustability in it so I can tweak the position for mis-alignment quite easily.
Checking driveshaft position
Next, I bolted up the subframe so that I could check the diff position and the driveshaft position. I used some steel tube that fitted the output covers quite well as a substitute for the driveshaft.
The rear sprocket clearance on the subframe is good also. I cut the section out so I could have plenty of room during fabrication. I plan to add some steel back in to reduce the hole size and add some strength back in.