Hi. If those are your plans then i'd suggest that you look for an alternative rodkit.That isn't to say that the repro kits aren't any good,i'm sure they are,but they weren't designed for what you're going to be asking of them. I'd suggest you check out the Samarin catalogue...they have a Montesa/Bultaco 250 rodkit that will almost fit right in..the mods required aren't that hard..and is of the quality (silver plated cages etc) that you're going to need. They list various specifications...you need the very best.Fit these with new bearings and you should have a robust crank..the crank itself is quite strong with the oiling to the big end always,for race use,being its weak point.If you have machining facilities i'd recommend indexing the center pin,via woodruff key etc at 180 degrees..i'd also suggest skimming all the wheels,inner and outer faces as some tend to have a bit of a "wobble" to them, to a dimension and having them balanced using the new rod kits/pistons you're using.Good luck.