My 883 A65 makes 73ftlb @ the engine converting from rear wheel not running at its best. You only need hp and rpm to find torque. You can convert rwhp to engine hp, as used by factories, by multiplying by 1.134.
The BSA factory had a 770 making 78hp @7000 that's 58.5lbft at that rpm. It's torque peak would be at lower rpm. My friends A65 750 long stroke works out at 63ftlb at 5000, 62.8 @ 5,500, [email protected]
6000 and 68hp, but there it ran out of breathing and power fell at higher rpm. So 45ftlb isn't very realistic for a tuned 750 A65.
Even if you were based off rear wheel hp torque can be 55ftlb + for an A65 based 750. Though spread and hp are important.
So a 300lb A65 750 could be floating easily around 4.76lb per ftlb. But it needs hp across a big range to get the best out of it and a big flat torque curve.