Well on the A70 it's an odd one. It's the one everyone denies any involvement with!
By 1970 everyone inside the factory knew the short stroke was the way to go. It was easier to get a big engine using an A10 crank - Vincent, Brown, Norman Hanks and Mick Boddice all did it - but the short stroke was better in engineering terms and would have been cheaper to produce. Les/Dave Mason worked on this - all un-officially of course, like everything else good at BSA! - while the A70 seems to have been Clive Bennett's baby. Bennett probably saw what the sidecar racers were doing and thought;
"That's the way to go then" instead of asking them;
"If you were going to produce a 750, how would you go about it?" But that seemed to be standard management practice in BSA. The management never consulted the shop floor.
Dave Mason put Les Mason's first short stroke A65 in a Rickman frame and used it to beat Phil Haslam to the MCRC Open Class Championship. If you don't know of Phil Haslam he was the fast one. The one destined for stardom (but was unfortunately killed, passing on the mantle and his bikes to Ron). Les offered the engine to BSA to bench test and was told he was only a draughtsman and should eff off! Mal Carter - the Haslam's wide-boy sponsor - of course came round and tried to make them an offer they couldn't refuse, to buy it! A bit sad that a Yorkshire second hand car dealer saw more in it than the management at BSA! But then there wasn't much chance of Lionel Joffe being seen at a race track!
Saying all this I've talked to both Dick Mann and Dave Aldana and they loved the A70 as a flat tracker. Dick Mann used it for the final races of the 1971 season, when he won the AMA title, and said when they got the A70;
"It was like cheating." But you do have to ask yourself, as the USP of the A65 was that it was a short stroke motor - the only British big short stroke motor - why with the A70 did they revert to a 1950s bore/stroke ratio? Mind you, I've never ridden one. They could be the Dogs do das
So yes, they'll be stuff on the A70 but not too much on the technical development history of the engine, as all the factory people I've interviewed (and it's 40+) have denied any involvement. And this includes Peter Brown, who was the main A65 development engineer! I think that speaks volumes.........................
Cheers
Pete