A few more paragraphs would help immensely.
Enough about that.
I am a bit confused about the track your talking about. Can you post a pic of it?
As to U-bolts. Depending on the kind it is a possibility but not recommended even if they are heavy. Muffler clamps are a NO NO, I have seen it done.
2 things to consider. Load dispersion and frame interaction.
You want the stress to travel through the track/risers and to the floor in the largest area possible (the best way of thinking this through is that the system is like a waterfall going into a pond). The more mounts you can use the better (less pressure than 1 stream of water). The frame already have a mounting scheme that was engineered for this function. The more you use it the better. You still only are doing it halfway correct because the floor was engineered to carry the load from there.
The more you spread it out the better. This makes each anchor less critical. Once it gets to the next layer (Floor pan) the load needs to spread out. Putting (welding) a large 1/8" plate underneath with as big of a footprint as possible will spread out the load over the surface (Think about what happens when you stick a screwdriver though a hole and rock it, this is called a MOMENT ARM). It doesn't have to be a single plate for all but the larger that each mount loads through the better.
You also want to control the path, a U-bolt has the potential to allow the part within it to rotate (loss of load direction) you are better to weld a tab to the structure and pull the strap with a bolt on either side (Bigger the seat and occupant, larger the plate and thickness)
Fastener types should be no less 3 and above with correct torque applied and lock tight should be added to all. There should be no less than 4 full threads at the bottom of the bolt.
You don't want to mount to the frame of the vehicle (unless its a UNI-Body and that is a whole other discussion), people do this and I cringe. I know that alot of old cars had it but they crash tested the system and you haven't. Reason being is that if the body takes the right hit and the body metal is thick enough it CAN CUT THE BOLTS. BAD RESULTS
Seat mounts are critical and I am not aware of all the details on your app. so these are general comments.