Quite a common thing to do on older vehicles with glass fuses. Has been documented before but here are a couple of photos I took last year when I did my own 1986 90.
When cutting back the wiring I was pleased to find that it was all clean / shinny copper with no corrosion.
The fuseboxes are easily available on-line from VWP, Ebay etc and require only a tiny bit of trimming of the mounting plate to fit.
Did it on my 200Tdi 90 some years ago, partly to get rid of some faults, but also to expand the fuse options for future projects.
So, if you can, consider an extra fuse board. Most important though is to label and photograph EVERYTHING, especially the wires that you think you will remember.
@Alpinewoodsman , same as @Litch, recently changed mine over - it's a very straight forward task. You'll note the fuse holder units are 8way, the original glass fuse holder is 6way. This is a bonus giving an additional 4x fuses