Hi Mike,
And welcome to the forum,
Ive not been a member very long myself and i did move from Mid- Wales (BALA LAKE area) to here france,
Like you ive had a rook of bikes and still have 6 now, one being the BSA 650 Rocket, and again like you ive nearly cried when i think of the bikes ive sold in the past after spending time & money getting them up to A1 condition, "hence i put a stop to selling on the bikes and just kept them".
Ref the fuel for the BSA, the one i bought had had a complete engine strip/ etc from a well known racer at the time a bloke called 'VIKERS' and he'd put new hard top valves in this BSA, so ive not had to worry about the fuel, but i not honestly know what the original valves we're ie hard or soft.
Having said this ive an classic citroen 2 cv and its the original engine in it and these cv's we're made with hard top valves from the first editions all those years ago and this car has unleaded in it all the time,
If you want to get hold of your local branch of the BSA owners club im sure one of the members will be able to give you some sound advice ref this one,
just google BSA owners for your area and you should get the contact details,
It's better to get details from the likes of these clubs and sleep well at night rather than not being sure? Even think about joining the BSA owners if your not already a member.
But back to the BSA you've got, Great sounding bike and mine is a joy to ride, You've picked a good classic one (keep hold of it