Nice work so far. I have a 62' Safari and it had a few drill holes in the cross channels which I reused replacing rivets in critical places which really helped tighten up the metal. The cross channel is relatively thin as you know and easy to drill a few more holes and use the large belly pan rivets.
So my opinion is yes, you can drill in the cross channel.
Mostly it is just the middle flat piece but on the SS the next rivets up are on the side so if we end up replacing the front or back end behind the wheel the aluminum will have to be cut away or replaced in that case it have to be formed. Any Suggestions? I do have pictures but I am just learning how to navigate and I am not to savvy on to incorperate the pictures yet.
Rosie the Riveter
If the piece that you are talking about is a simple curve you will not have to do anything fancy to form it to fit. The aluminum is flexible enough to form around the curve by hand.
Only he who attempts the ridiculous can achieve the impossble.