I've got such a set up on my Herald 1200. The factory kit is
essentially a Spitfire mk1 set up, with 2 HS2s, an inlet manifold with a
bolt on balance tube and a cast iron exhaust manifold.
The Spitfire mk1 camshaft is also part of the upgrade, for cars that
don't already have it. Origonally only 12/50s, and export 1200s had it,
but after a certain date it was fitted to all 1200 engines
I've got the full details of the factory option in the parts catalogue at
home which I could photocopy, or maybe even scan if you need it.
It lists a special exhaust system for the twin carb, although the 12/50
system is straight fit as the exhaust manifold is the same dimensions as
the exhaust bit of the 12/50 manifold. It may be possible to convert a
12/50 manifold to do the job, in theory. The home market standard 1200
manifold is different though, being shorter with a small bore outlet.
Most export 1200s had the 12/50 type setup though, I believe.
The throttle linkage on mine is non standard, using the existing cable
with an additional anchor point on the balance tube. The parts catalogue
will describe the standard setup.
Keith Bennett Keith.Bennett@bbc.co.uk