Gas, tires, oil.

Regarding my soon swap of a 14 bolt into the suburban, Mike writes: Did you have to change the length of the rear driveshaft?? I need to know ASAP b/c I am considering the same swap in my 1986 K10 truck. What do you think of using a FF vs a SF rear end? I could really use some advice as I am considering making the purchase this week.

I haven’t done it yet (this weekend hopefully, finished the front axle last weekend, many post to come), but the driveshaft should be fine. The length looks the same within an inch (from the center of the axle to the u-joint) and I think the u-joint is the same (if not you can get an adaptor u-joint).
Now, full-float vs. semi-float (K5 has a lot of info). Full float is stronger, but semi is OK unless you have a big block and large tires and a lead foot. Full-float is only availible in 8 lug, whereas it is possible to find a 6 lug semi-float 14 bolt (however, only in ~’90 up heavy half/light 3/4 trucks and the spring perches will have to be moved to fit the older trucks). If you are going to install a locker, it is many times cheaper for a full-float (you don’t have to replace the carrier, unless it already has posi, so check first). The full float does use larger u-joints, so be prepared to buy the adaptor. The full float doesn’t have c-clips so if you break an axle you can drive on it. The full float is larger and heavier and will have less ground clearance. More on FF here.
I went with the SF because I just wanted bigger brakes and better towing capacity than the stock 10 bolt, and I could keep the stock rims.