If you have a blank body and a fully assembled body with all hardware attached, and a gram scale, then it is possible to calculate the weight of micro-balloons required to add to the resin mix in order to achieve neutral density.
a gram scale with 0.01g increment would be nice, but 0.1g would definitely get you close.
The solution is complicated and so I have written a spreadsheet to make it simple. You will need to read up the post on Archimedes dunk test but it is really not difficult, as others who have tried it will tell you.
If you or anyone would like to try the spreadsheet then PM me your email address and I will send it.
Dave