Do you have the neutral light working? I put an MC21 motor into an MC18R2 chassis and had to hook up the neutral wire out of the GPS.

It does sound as though you have the complete motor if you have round bores and a GPS.

This is a pic of 3 bottom ends and the MC21 on the left has a hole for the GPS cable where the other two just have the neutral connection.

More pics of the internals of the knackered motor if you can be arsed.