<VV> trans mount replacement

[6spyder4 at comcast.net]

I'm new to VV, and could use some info on replacing my 64's trans to rear cross member mounts.  Picked up a set at Ventura so got to get busy!  All research I've done seems to assume removal of the crossmember--and all that involves. Problem is,  the bracket bolt heads aren't tack-welded in place, and the 2 front ones can't be held to remove the nuts from the bottom.  I know I'm not talking about an unfamiliar problem -- so anyone have a tip how this could be done without dropping the whole crossmember??  I've even debated cutting a hole thru the floor pan over the bolt heads--but rather not do that.  Maybe loosen the bolts holding up the crossmember a little to get clearance??
Anyone have an idea, or experience in this?   Thanks, Nick