I would run the biggest single on a tuned pipe on all the nitro I could shove into it and probably have it running well into the teens rpm wise
Any of Those twins would fly apart treated like that . plus NONE of em can breath as much as one can get with a huge single - -simply can't get the flow thru the passages .
Design wise they simply are not ready for that kind of abuse
Look at old Kart engines - I use Mac 10s years back - these can really take a beating.
Now -If'n yall like tractor pulls -and you have a Satellite /cable TV- tune into station RFD -and watch the pulls and old time tractors n saw mills n simply great entertainment for thos who love machinery
I watched a guy blow up a Minn.Moline - the low end came apart - some of th e pulls are Unlimited class -stunning power.
(Somehow I just KNEW that Pe secretly wore klompfers Ja!)