Thanks Phil.
But I should have said it's for a bias pedal box so I'm just after a single cylinder, not tandem.
Good news is that Compbrake are back in business and not too far up the road so I'm collecting one from them in the morning.
http://www.compbrake.com/product/mas...-0-875-remote/

Remote reservoir type but they do a reservoir which does screw straight into the master cylinder (if I can squeeze it down far enough for the front clam to close).