Lots of kits out there, but I ended up using a stock wheel tub and just had the factory one cut off, left a few extra inches and attached the new one. Guy I bought it off of did the work. Turned out very nice. Looks stock from the trunk. The coupe's backseat was modified slightly and the FB needed the tub to be clearanced just a little for the fold down back seat.
I have a Autoworks International kit that I didn't use if you are interested. PM me and we can see about a price. Using the stock tub is cheaper, but takes a little more skill, from what I can tell, to get it right since you are just picking a point and cutting. The kit has a few more instructions.
Here is a pick of a '66, tubbed with 315s on 18 x 10s. These are the same rims, from the same guy, that are on my car. He kept the springs and used a Crites Spring relocation kit. The FB got a 4 link.
Either way your rear end will need to be measured and cut down once you get your rims mocked up and determine the length.
1968 Fastback: 331 stroker, FTI cam, N351 Heads with a few upgrades, 4r70w w/3600 stall, 9" locker w/3.70 gears