I recently bought a used Lawrence 120 that had some stitches coming loose at the belt loop stitching.
Rednichols, turnerriver and others gave me some pointers and advice on how to fix it. 5 cord waxed linen 25 yards from E-Bay) , harness needles (John James # 2 from E-Bay) and a saddle stitch working thru the open top. I used a home made awl to poke thru the existing holes.
Before
After re-stitching then touching up with Black Rock
Boy; while it came out pretty good this is harder than it looks. Per advice I cut the needles to half their length and filed new tips- I should have cut them even shorter as I had to mid project. The No 2 needles were for up to a .8mm cord. It works but it sure was hard to get threaded - but doable. I am glad I didn't get bigger (Tandy?) needles as it was hard getting thru the holes as it was. One needle broke at the eye when on my last back stitch and I ended up with both ends on the same (inside) side at adjacent holes. I just tied it tight and called it a day.
Advise:
Progressive Bifocals, slipping down your nose do not help.
Get good lighting, a visor or head lamp would have helped in trying to see the stitch holes inside.
Cut your needles just long enough to get thru the layers ok and file a tapered ( but blunt) point. By the time I re-cut mine I was already started and didn't take time to re-profile. I should have.
Have a decent slim leather awl. My home made one worked but was a little large and kept slipping back in the pin vice I was using.
Use Needle Nose pliers to grip the needles, especially inside. Locking ones or Forceps might be even better. You won't be able to sew from the inside without them
Take you Time.