I plan on adapting the newer sending unit to my stock tank (89 K5 w/TBI) for my swap. If you have a brand new tank you can have a shop weld an adapter ring to it or if you're using an old tank you can use some two part epoxy and small hardware to mount the plastic locking ring area of the donor tank to your steel tank (that's what I'm trying first). NastyBuzzard showed us what both of those methods look like in his build thread:
http://67-72chevytrucks.com/vboard/s...=627161&page=9
The TBI sending units are already pretty crowded and I don't think you'd be able to find enough open real estate to mount the FPS on it. You may be able to mount it somewhere else on the tank but I'm not sure how far it would stick up or if you'd run in to any clearance issues once you go to mount the tank back up...