I would be tempted to completely and neatly fill the old hole and start again - especially as the old trem wasn't very nice
This is slightly involved but it gets the neatest job in my opinion
Please note that I have a lot of experience in using routers and power tools and they MUST be treated with care and respect - hurting yourself is not part of the planWhat I would do is have somebody make me a matching pair of templates to a shape just bigger than the existing hole (a male/female pair that fit inside each other).
Almost like a square jigsaw piece that fits perfectly in the hole in the other piece.
They would use a CNC roter to cut these and it may be expensive but it will get the neatest job
Typically I have had these made in 3/8" plexiglas (
www.Simscustom.com have been great in this capacity)
Using a router and a cutter with a bearing follower I would position the female template (the one that is the hole just bigger than he existing hole) so that I could cleanly cut out all the bondo and rough wood to leave a clean hole just as deep as is needed to get rid of all the cr@p, or just as deep as the piece of wood that you will be using to fill in the old hole
Then you would be able to fit the male part of the template into the hole if you wished and it would be a snug fit.
Take a piece of matching timber (mahogany) just deep enough to go deeper than the old hole used to be and cut a piece exactly the same shape as the male template.
As I have an inverted router table I would actually use a bearing follower router cutter to get the block I will use to fill in the hole really snug to the template.
So I will be left with a neat hole in the guitar, and a block that would perfectly fill that hole
Glue the block tightly into the hole and once dried level perfectly to the top of the guitar
Now you can either drill or rout for the bridge of your choice
Yes I have skipped a lot of the considerations needed to execute this job totally but I just wanted to give you the idea