You don't necessarily have to have frame connectors going through the floor. Tieing the 8 pt. roll bar into them with the angled bars off the main hoop, behind the seats, will help a lot. If the connectors touch the floor anywhere, they could be tack-welded there as well.
A 2.71 low gear 904 may be too much for the stroker and small tires and make it harder to hook! But do get the tallest tire you can and install on the widest rim that will fit (i.e: 9" tire on 9"-10" wheels.). A taller tire actually puts a little more "footprint" on the track. But you may have to make up for the height with more gear.
I'm not surprised that 15 year old tires spin downtrack. I'd consider that a safety issue.
Make sure your drivetrain is up to handling the "hook" when you get there. Hopefully you have a driveshaft loop. But I like to use Spicer solid u-joints and a billet steel rear end yoke because OEM versions can eventually start to spread when abused.
Sometimes to get some consistency, one has to break down and add weight in the trunk.
Consistency wins bracket races and gives you more time and money to figure how to go faster.
I've run 11.50's at 112-113 mph with 1.50 60' times. That shows that you have some tuning and matching of parts to work on to get the combo more efficient. (Carb tune, converter, gears, shift points, etc.) Just getting it to quit spinning down-track should help mph. But you seem to have a good base and on the right track with a lot of good advice in these threads.