Whoa, slow down mate, 15years ago I bought a Super Rocket with a rumble coming from the bottom of the engine, I too had heard of the timing side bushing problem, so long story short, and $2000 later the problem turned out to be worn splines on the drive side of the crankshaft, the drive gear on the primary side rides on a sleeve that meshes with the crank on splines. So before you do anything rash and spendy, check to see if there is much play in that sleeve to the crank. I fixed mine by taking some 6 thou shim stock, cutting it into strips and sliding them in between the splines, no noise now or the subsequent 22,000 miles since. However "Goldy has a good suggestion on checking the up and down play on the crank. I'm not putting down the SRM conversion, I did it and now glad I did, but it wasn't necessary in my case, a regular plain bushing works just fine as long as you change oil regularly, and are not racing the bike. Good luck with your motor.