Hiya.
We use cast ally Girling cylinders. They were used on some Reliants. Others used pressed tin ones, (nowhere near as pretty -they look like baked bean cans).
5/8" bore seems to work for us. Ska Man's, Flap's & Simon's use a single line from the cylinder, split via a brass T piece to feed the front & rear brakes. We've had a few problems getting the lines to seal against the T piece though, so when I plumb in my own I'll use a double length banjo bolt in the cylinder with 2 independant lines, one going forward to the single front caliper & the other back to the off-side rear. Then I'll link across from there to the near-side. That's the way the standard Reliant system's done.
We don't use bias or proportioning valves, but the front brakes are old 70s single piston calipers, (mine's a 250 Superdream one). The rear discs are more efficient so pull up quicker than the front, which is the way you need it. If your front brake's too good on a linked system you'll be constantly locking the front up & nose-diving. A locked front wheel also means no steering!
Have a look in the brake section of Merlin Motorsport's catalogue for the cylinders.
http://www.merlinmotorsport.com/index.php
