Hi
This is what I did with my old 1302.
Regarding tyre size, you would be surprised how close 17 inch tyres are to stock tyre heights. The speedo that I used was a really old Stewart Warner, the SW stockist made a ratio box to correct the speedo, the later electronic speedos are much better in this respect as they can be adjusted for various wheels. If you want an accurate speedo at low cost you can always get an electronic speedo from a push bike.
This what a friend did with his car, monster tach where the speedo was and a VDO electronic speedo in the dash grille.