is this at all possible weird

hello and cheers for all the input, i did my piston stop thing just to give me a ball park figure,not ideal but the rotor pointer on dizzy <when it was inserted into spark plug hole> was bang on the number 1 on the cap and when checked balancer no marks anywhere near to be found,i have no tacho wired up<i should> but bet you where the stumble clears its at the same increased rpm point every time give or take i think timing chain out would run crap right thro, as would sticking valve etc, the transition is so precice like its running with several plug leads off then they all reconect at same time.for piece of mind im going to swap out the balancer for the potential damage can cause if is slipping which im sure is the problem.stationary the car revs up sweet,only under a bit of load, it has run very well in past so im leaning on it being an ignition timing problem. ps any suggestions on a brand/supplier of balancer? have to get one stateside for sure