Nice! I have two old Singer sewing machines. I use them for making sails, as I have a wee yacht and sailing dinghy. They go through anything using a denim needle.
Need to re-trim my rear seat using the old seat I have to match my front seats out of a Pug 106 Gti.
That was a lucky find you had there!
After doing a bit checking I will need a proper leather needle as it has a chisel point to cut through the leather. This would be bad on a woven fabric!
The machine I have is a Singer 201K from 1957. Stripped it and refurbished it and it works a treat. No fancy stitches, just forward, reverse and variable length stitches. When you strip one of these down they are an amazing piece of engineering and manufacture.
I picked up a set of Alfa 147 seats (fabric) and like you I will modify and recover the rear seat.