I would like to know how hard it is to convert a Lister TS2 from a generator to variable speed.

Hi all.  I have a question, but first a little background.  A bunch of years ago, thanks in no small part to Rocketboy F1's excellent website, and a loving and understanding wife, I found myself in possession of a 12/2 engine.  Now here is where the fun starts.  The engine is internally counterbalanced.  The flywheels are the 6/1 counterbalanced type.  It seems to me that I need to "un" counterbalance my flywheels.  I have toyed with the idea of buying new ones, but a big part of me wants to solve this problem.  I have debated using an angle grinder to grind out the weight, but from all that I have been able to gather that is a messy, time consuming, fraught with potential failure kind of idea.  My son (a MatTech in the CF) gave me an idea. What would stop me from putting a bunch of lead opposite the counterbalance and effectively oppose the generated forces?  I really don't know.  What say ye?