I found this company while surfing the 'net. Prices seem reasonable. And they specialize in exhaust for Windsor-based setups.
180 Degree Headers for Windsor Motors
I require a Hewland LG 500 (4 or 5 gear) gearbox and have a Porsche G50 and ZF 5-25 gearbox in good order plus £s .. to swop for a reasonable condition one.
Any one out there with one gathering dust please?