Hmm... interested in the same. I'm "building" a poor's man fretless with my old Peavey Millenium EXP 5 stringer.
I've seen the size of these pus are a bit smaller than mines (supposedly standard J, but not sure) so they should fit in the hole, though leaving a little gap on the sides (10cm vs 9.5cm aprox.).
The thing for me is the position of the screws, which in mine are a bit more distant between them. I guess the fix is easy but for sure will not look good :s