Re: Replacing a Floyd Rose. Suggestions?
See if Floyd Upgrades has a huge brass insert that will fill the entire cavity, and provide pre-drilled holes for a 4-bolt hardtail.
If not, invent one.
However, as was said, filling a Floyd route is a lot of work. First, if you've looked at it, it's got rounded corners, and not very well-rounded at that. Making a block to fit it will have to be done on an individual basis. The cavity may also require a certain degree of refinement to make it fillable - squaring the corners, flattening the sides and bottom.
Then there's the hole for the block, and filling the post/insert holes.
Tonally, there shouldn't be much difference because the amount of wood removed in the first place is probably equal in weight to (if not less than) that of the bridge, claw, and springs that replaced it.
The biggest change in tone will come from the filler used. Don't jam a mahogany block in basswood thinking you're going to get a rich, warm, fat LP tone, and don't jam a block of pine in there thinking you're going to get a nice basswoody tone.
You could also consider Plaster of Paris as a filler. Maybe find a recipe for making piezo-ceramic paste and have an epic-huge piezo pickup.