Hey Rosco
Sounds like an interesting project, your BSA Speedway bike, just had a look through the article in the magazine , Australian Speedway News , issue 55, and it mentions that the gearbox has been lopped off and a countershaft fitted, recirculating oil supply retained and total loss battery ignition, no doubt these days the ign could be improved.
As I said , try to get in touch with Dutch through the forum, as he seems to be a bit of an authority on unusual Speedway and Longtrack engines.
Good luck with it, let us know how you get on .
Foss