Here's a couple of options to get you cast 15x7's with a bit more backspacing:
Halibrand can machine these to 4.25" BS, 1/2" more than TT D's
http://cgi.ebay.com/ebaymotors/15x7-Hali...s#ht_1165wt_912
Vintage Wheel Works V45s have 3-7/8"BS, so another 1/8". Maybe not enough.
http://www.vintagewheelworks.com/pro...heels/v45/15x7
Team # has their 5 window 15x7 available with 4.75"BS, which would essentially put the entire extra inch inboard compared to a Torq Thrust D 15x6 (w/its 3.625"BS), but not sure if there will be clearance problems with tie rod ends, sway bar, etc.
http://www.team3wheels.com/et/classic5.html#
Finally, American's new versions of the T70R Torq Thrust have 1/4" more (4") backspacing in the 15x7 version compared to the Torq Thrust D or TTO
http://www.newstalgiawheel.com/wheel...ubcat3=1011128
'69s need all the extra backspacing they can get, too, even with their bigger wheelwells.
Good luck!