63 C10 dropped what size wheels

[63frankintruck]

Guys,
Going to order 700R4 SS trans from Phonix Trans in Weatherford Tx. soon. They want to know what size stall I want and what size tires I will be running.
Currntely set up with 2.5 drop spindles 2. inch drop springs and some type of drop springs in the rear from PO.
I using 15 inch rollers on the truck now, but was thinking of going to 17" wheels of possibly bigger and definitely wider tire that what I'm running now.
My question, what size tire can I be running without a bunch of modification (just not sure what is possible current configuration, so I can tell the trans builder.

Also, how big of a stall convert should I be asking for? (L31 crate eng from GM, with ramjet or vodoo cam)
Thanks for any and all replys!
Dan