Sounds like you have a pretty good setup to have fun with. With the smaller tires and stock style suspension, I think that the powerglide was the better choice for being able to hook. With that said, you do need to put some upgrades in the trans to make it live. I would suggest the dual ring servo, billet servo cover, kevlar band, hardened input shaft, steel hub for 6-7 clutches, drum drilled with holes under the band, and have the front drum cut for the front roller bearing.
I think that those heads will work for the naturally asperated up to about the 7200-7300 that you stated, but will be a little small for the nitrous. I am going to take a guess that the ET could be about 10.20's in the quarter and about 6.50 in the eighth.
Good luck,
Bill M