www.britishvacuumunit.com

jeg's spreadsheet tells us that the spec for a 37H8226 unit is 3-9-8.  This means advance starts at 3lb of vacuum, is all in at 9 lbs and has a total of 8 degrees of dizzie advance (16 deg crank advance).

I suppose you could just find a unit with those advance specs - and which physically fits your distributor body.  

I have an Aldon Yellow (which I think uses a 49D4 body... Aldon helpfully grind off the original ID numbers   which my Guru decide would benefit from a vac advance unit.  He rummaged around on his shelves before deciding that "this" was the one.  Before and after checking showed a 30% (yep - 3 zero) improvement in touring fuel economy...)

Cheers, Ian

A poster in another thread dealing with vacuum unit types mentioned using a Ford unit as a replacement for a Lucas one.  I've been searching for some time for a  37H8226 vacuum unit for my Lucas 59D4 41882A and wondered if someone had found a replacement unit that would work well?

Jack