Paul Rosche story
I don't think that they had balance shafts. At least I cannot see that in the above picture and nothing is mentioned in the story of the engine told by Paul Rosche himself. The engine did 11.000 rpm in race trim and made 1000 bhp available. In qualifying for one lap they could activate almost 1400 bhp, but the upper con rod eye would have been stretched to one additional millimeter.
Their biggest problems were cooling of the pistons which they did by injecting castor oil into a cooling channel in the piston. The other problem was knocking. They had no control over the proper ignition until they used an old trick of WWII aircraft engines. They used methylbenzene C7H8 for fuel which is poisonous like hell but has supreme knock resistance.
If you build a similar engine today much of the material selection will be different like the engine block which was made from cast iron. Today they would probably use cast aluminum alloys.
The specification detail from gurneyflap show that the engine made the power from the turbo pressure and not from the rpm. They went from a 3 bar standard pressure to almost twice that with 5.5 bar. But the engine would do this only for one hot lap. So quali engine life was probably less than 20 km.
I would not know what the FiA will be going for with the new engine other than a certain power level and best fuel efficiency. We know from Norbert Haug that target power will be 600 bhp. It means that the old BMW engine would be running well below 3 bar turbo pressure.
I believe that the emphasis could be on higher revs (higher revs make for better efficiency) like 13.000-16.000 depending of the harmonics of such an engine type. I know very little about the harmonics so someone who has experience in race engins should say something.
I would find it totally impossible to run with special fuel again as they did in the eighties. We would most likely see standard grade petrol with 5-10% bio fuel added.
My assumption is that the peak power will be limited and that the development race will be for the best fuel efficiency in partial load conditions. The team which runs the leanest engine under partial load will have to carry the least fuel and will have to detune the engine latest.
So variable valve timing for avoiding pumping losses, exhaust gas recycling, stratified direct fuel injection, ion current measuring and all the modern technologies for increasing the combustion efficiency should all be employed.