Advise /help required from Electrical gurus

Hi

Nearing the end of Resto of series 1 1.3 golf

When I got the car it had a mk2 1.3 engine in it.

It has now been changed back to the correct 1.3 GF engine.

However, there is now problems with getting it started. 

Initially the mechanic couldn't get a spark between coil and dissy.

He had an auto electrician out to it. He managed to get a spark (only temporarily) but says that the ignition system is positive but the distributor is negative and that is causing the problem.
I don't understand electrics at all, and we are at a loss of how to overcome this problem.

Any advice would be greatly appreciated 

Just realised the car has an ignition module fitted. Did 1980 Golfs have these fitted? Has this been added when the mk2 engine has been fitted?