This is a trick I worked out on a previous boat. It guarantees perfect alignment and placement, but only works before the deck is put on
The studs are assembled onto the footbraces (don't use the fiber nuts that came in the kit, save them for the final assembly and use standard nuts, instead) and the whole assembly is glued to the inside of the hull using the standard woodflour epoxy mix (mix it thick). The clamping system is effective, yet simple. The plastic sheets are there to catch drips.
Once the glue has cured, remove the footbraces from the studs. As you can see, for the initial glueing I didn't use much epoxy. Wrap plastic packing tape around the threads to keep them clean.
Here the stud has been bedded in epoxy and covered with a patch of glass. Note the orientation of the patch. This way both sets of thread (warp & woof) share the load of a foot pressing forward. If the patch had been installed with the sides parallel to the sheer, the vertical threads would have made little or no contribution to carrying the load. This orientation is approximately 50% stronger.
Just as with the taped seams, the glass is the primary structural component. Therefore you only need just enough putty bedding to smooth the transition where the glass goes over the stud. Any more is wasted weight.
The footbrace fits perfectly over the studs. It's ready to be bolted on when the boat is complete. In the meantime the threads on the studs need to be covered with plastic tape to keep them clean.
The hull is now ready to be joined to the deck (after a bit of trimming on the bulkhead, of course). The seams are taped, the stem & stern pieces are in, the interior is completely glassed and the footbrace studs are attached. Good to go.