Hi Ive had the SRM needle roller convertion, its a good modification if you can afford it.
I live in England so i didnt have any problem, they took my whole bike away and
they did a first class job. My crank cases dont have matching numbers either,
the plain bush is alright but like any bush if you dont change the oil regular
it will ware and also when it does ware it starves the crank of oil then it can throw
a conrod through the drive side casing which might have happend to your engine,
here's a few pics of my bike, I took them at srm during the rebuild.