Well Novak sells an adapter..
That's about 4" long or so.. I thnk.
The OEM chevy one is 12" long or so.
But the tranny is only 12" long, and the D300 is wayyy... shorter..
Drag whatever engine your using as far forward as possible.
Measured out.. I'm still about 12" or so shorter then my current setup..
But.. IMO it would be easy to cut down and weld up the OEM adapter.. and at a dime a dozen.. I wouldn't be hesitant to try.
If you did that right, then re-splined the SM465 shorter.. It wouldn't be a stretch to venture a guess that you could be installed for WELL under 12" shorter then what I have now.. maybe 18" or so.
No website yet.. this is just me farting around with adpters trans and t-cases.