I have loved reading this thread, because it just goes to show what development and enthusiasm can achieve. I have always thought the Bullet is one of the most underrated bikes of all time. I wonder what could have been if Bill Lomas had stayed with Enfield and the company had the foresight to fully develop the d.o.h.c. engine. Looking at the race results, what ever happened to that fast B33 B.S.A. made ?. I think it was called a gold something or other. (Tongue firmly in cheek).
I personally believe that the pushrod valve gear can be(and has) improved to the point that it can do as well as OHC up to the rpms that these relatively long stroke engines can operate up to. There are pushrod drag racers and NASCAR racers which push 12000 rpm on pushrods with extremely high spring loads. I will grant that this places a lot of stress on that kind of valve train, and it might have short life, but it can do it in a racing application and be successful.
I consider the DOHC format more necessary for engines that rev higher than that. In our case, the valve gear is not the limiting factor. The limiting factor is clearly that we are running a longer stroke length than anybody else on the track, and that is highly stressful to the crank, including some breakages. The valve gear is handling the application, so far.
Now, with the pushrod vs DOHC situation, there are some advantages to the pushrod over the DOHC, particularly in vintage engines where the cams are physically located at one point above the valve buckets and cannot be moved. The cam buckets have a certain diameter, and the cams sit a certain distance above the buckets. This limits valve lift, and also some other things regarding valve motion. There is no form of "ratio multiplier" that typically is employed on these DOHC engines with the cams over the buckets. And even in some SOHC situations, the ratio is fixed by the dimensional layout of the parts.
In our Bullet with the pushrods, we were able to add a significant amount of rocker ratio with our package, and increase valve lift to over .600" , which AFAIK is higher lift than any of the competing engines with OHC can manage. So, in our case this pushrod package actually gives us an advantage over the OHC engines because we can lift higher, and the valve train can withstand the application of just as much revs as the others. With a shorter stroke length similar to theirs, we could reduce the crank stress and raise the rpm range to equivalent to theirs, and quite possibly then have the power advantage. Racing is all about pushing limits till things break, and then finding ways to push them further.