Iain,
You have an A1 chassis, it uses the complete front sub frame from a Cortina bolted onto the wierd front chassis T piece. I would think that Cortina sub frames are a bit difficult to find nowdays, except that I have the one I got with my chassis, unused and complete with steering rack and 5stud hubs, OK for a road only car.
If you can arrange collection you can have it gratis /ubbthreads/images/graemlins/grin.gif It has had the strengthening mods done and is ready to fit.
I did have a pair of rear trailing arms, but I threw them in the skip last month /ubbthreads/images/graemlins/frown.gif
Dave
P:S Have attached pic of rear of KVA A1 chassis(not mine)