Althought it's a long time ago I ran my 705 with TC body, you can really tell the GTP body adds downforce and stability! I'm going to try some things in set-up next time to benefit more from the added traction. But first see what the floating body mount does for the car.
Superglueing is what I'll do if this doesn't work out:
http://www.mytsn.com/products/desc.asp?prid=2397
Spray it in the same colors and it should cover the old bodypost holes.
I wish I could hit the track tomorrow, or coming weekend... But I won't have a weekend off for the rest of the month.