mike
i guess you could go to a 45 blower roots
4005 tri lobe
maybe at a push you could drive a 47
is the engine water or air cooled?

i think roots blowers are based in hull.
i know you like tinkering with engine,s but why dont you buy a cheap tm & do it up in your own time.
building your own unit can work out a very big head ache & quite a bit of cash.
Lee G
new blowers cost approx £1000/1200 for a 45