If you really want to do this right, i suggest the following:
Put your whole rig together without floats, but all other hardware fittings.
Use a fishing scale and some string and weigh it in a trash can of water. This is how much buoyancy you need.
I use Inon floats plus a few Stix, but ULCS is no different. They all publish buoyancy specs for fresh water. You're weighing in fresh water, so everything matches.
Build a little spreadsheet with the relevant data to evaluate a solution.
If you bring along an extra Stix float or whatever, plus a couple of small fishing weights, you can fine tune on location.
I can get my rig, which is an oversized Nikon with lights, fine tuned to where it is neutral in the water below the surface, but at the surface will actually float [barely]. I've been doing this for a while.