I have done considerable research into this and talked extensively with Paul at Hydrotech. For all out bang for the buck simplicity the C3 M/C is the way to go (77-82). It has 1 1/8 bore and would work nicely on your application, and it's cheap. However it's a heavy cast iron beast and in my opinion ugly. The alternative is a C5 M/C which is lighter and nicer on the eyes but it uses some oddball threads at the M/C itself. They are 12 mm ISO bubble fittings. The C5 is also quite a bit more expensive to buy. There are change over fittings available for the C5 M/C but I have yet to locate them.
Thats all I know.
Noel.