Glad I checked fitment first, like a bonehead I completely forgot the research I did last year on mounting to the old Schwinns and just assumed it would bolt up without any custom mounts... d'oh!
So looks like I will mount to the seatpost using the stock mount, and have a mount welded to the front tube. My neighbor has a wire feed welder that he uses to make picnic tables, hoping to bribe him with beer to weld a simple front mount to the frame for me.
Something like this (I forget who I stole this picture from, but thanks for the example!):
I still have the flat mounting flange that came with my BGF kit, so was going to use that. For the tube section, would a piece of seatpost work ok? I have the 1" seatpost from my Cranny build left over, so I could cut that down to fit...