It's not particularly hard to do the ports by hand. BSA could have done the ports at least to how they were designed rather than short cutting at the factory, it may have been saving them a little money and keep the A65 on parity with the Triumph twin which they also owned. In 1970 they knew the difference between the heads but didn't rectify the production, they could have had 8 more hp in 1971. In their day these bikes were among the fastest most powerful on the road, but they were about to be displaced, or by 1971 they were being displaced by the 750s and the power bikes from Japan.
It was hardly a time to throw away easy hp in what was a full-scale hp race. You can see this when the mighty Z1 Kawasaki turned up, it was called the King. It was developed as a 750 but Honda released the CB750 4, getting the jump. Kawasaki held off releasing their bike till they increased the displacement to 903cc the reason they did that was to sell bikes, they understood the power of power. Honda claimed 67hp Kawasaki trounced it with 82hp and 54.2ftlb, though it was heavy at 542lb. For perspective my 883cc A65 weighs around 360lb and produces 97hp and 71ftlb it also has a very wide power spread. It uses a bigger version of the oval port above, so I'm interested to see how that translates onto an otherwise stock engine.
BSA already knew how to fix all the problems with the A65, roller mains both sides would have reversed market resistance, 71 or earlier they had excellent steel capped rods, high volume oil pumps and they had the A70 showing great potential. But they sank money and effort into things like the Ariel 3. And also the 350s that were a good idea though eventually scrapped because of a shot to the foot.
The 350 was a missed opportunity, they could not get good power from it because the head design was poor, DH had made an error, easy to rectify with a new casting, but management told him no. So 34hp was the best they could ever get. The 350 Honda was already in the market with similar power, the BSA 350 could and should have made 45+hp, and it would have been a winner, it could then be more expensive than the Honda because it gave more, it had the advantage with a state of the art frame and running gear already. A company like Kawasaki would have made sure they had what they needed to get the power necessary. So rather than spend massive effort and money fruitlessly down these paths, BSA could have done three things, fixed the A65 engine completely, and at the same time, because its basically the same thing, developed the A70And the third, built at least a limited number of Rob North style Rocket threes, the frames were state of the art and exotic, cheaper to manufacture than the std frames. The threes also work extremely well at 850cc if they wanted to respond to the Z1 and Ducati's SS750 when they came along.