Great build you've got going there. Only suggestion I would offer is to consider the LS swap with the new chassis. A decent pull out will get you going down the road quite nicely while saving the time and expense of having to reconfigure your set-up later. Going back in to rebuild the engine for more power later would be less of a hassle than having to go back and reconfigure for the LS swap.
Tim will certainly have more options/suggestions than I could offer, just thought doing the actual conversion while setting up the chassis would save you time and hassle, read 'dineros!'
On the other hand, having your car on the road while GAP builds you a stout LS would be way more fun! Decisions, decisions . . . .
At any rate, your in great hands at GAP. I hope to have my '72 there soon as well.
Starting installing the wheel tubs today. We took a DSE tub which will clear a 335 on the second gen, trimmed off the edge and moved it over an additional 1 1/4" to give him plenty of tire clearance for the 345 he wants to run