what gear/converter combo???

ok....eventually, I will be moving the rear springs inboard, putting in a 489 sure-grip, and a stall converter.......looking for opinions

It's a 400 with a .509 cam, Torker intake, will have headers eventually, and has 26" tall tires (275/50R-15 Drag Radials)I may wind up going with anywhere between a 26 and 28 inch tire....but that will definitely be long down the road, since the tires i have now are new.

I'm not sure if a 3.91 will be too much gear.....
I figure the TCI Streetfighter converter will be best.....
also, Randy's has a 3.73 set. just don't know.
I probably need to get it on the strip and see what it'll do and go from there???