If you PM me your e-mail address, I'll send you some files I've come across.
I've got the same box as you - my local machine shop has had a spare bellhousing for over a year now without them doing anything on it, so if you come up with a guaranteed mod to get the box to fit, let me know.
When I got my box, I had a long think about the best way to mod the bellhousing. Old document contents below:
What I’ve Got
TKO 600 Gearbox, part number TCET4618. GM spec gearbox.
Things to sort out/buy
Ford TKO nose length and spline length
input shaft bearing support for hydraulic clutch
prop yoke
prop length
clutch plate
T5 Bellhousing Problem
GM box differs from Ford spec TKO 600 gearbox by having a ½” shorter input shaft. The input shaft diameter, 16mm, is OK for the standard crankshaft spigot bearing, whereas the Ford spec input shaft diameter is too big.
For info, the T5 input shaft length is ~180mm long from mounting face of box.
Potential Bellhousing Solutions
1. Change the input shaft to a Ford spec one, and get the nose machined down to suit the spigot bearing. Weld two strips to the rear bellhousing face for the 4 mounting bolts, or buy a bellhousing already converted.
Issues: Cost of input shaft and bought converted bellhousing.
2. Machine 1 inch off the entire rear face of the bellhousing and replace it with a new face 15mm thick, machined to suit the input shaft central support and 4 box mounting bolts and welded to the T5 bellhousing. Reface new rear face after welding to ½” thick.
Issues: Ensuring correct alignment of gearbox to engine.
3. Do not fit the shitguard between the engine and gearbox. Machine 2mm from the from of the T5 bellhousing face. Also, machine 2mm from the rear face of the bellhousing. This would allow the gearbox to be mounted approx 6mm further forward than standard, meaning that there is approx 6.5mm (1/2” minus 6mm) less engagement of the input shaft into the crank (this looks to be OK). Two strips would still need to be welded to the rear bellhousing face for the 4 mounting bolts.
Issues: Input shaft is still approx 6mm too short (but should be OK)
Martin adds a 5mm spacer to the T5 bellhousing when using the Ford spec box