Honda-SOHC

I find my ignition switch accepts the key and turns and I can hear the contacts moving at the bottom, but its not making an electrical path. 

Most likely cause is that it's sat for a few years and the contacts have got damp and corroded away.

Looking at the switch the plastic housing for the contact at the bottom is held on by 3 plastic tags on the circumference of the lock, and I could possibly prise off the end.

If I do that, is the bottom 'contact' part available as spare ?, or is the whole lock fubar ?

Thanks, but it's not the clearance thats the limiting factor, its finding a radial that goes on a 2.5" rim.

The minimum rim for most (all ?) rear radial tyres is 3.5".  Hence the question, what other wheels fit ?

Would any of you good folks know if wheels from a later Honda or anything else, that would take a radial tyre, can be easily fitted (to a '83' SC-C), especially the back wheel  ?. 

Ideally keeping the twin discs up front and drum rear, but not absolutely so  ?

Many thanks

MC