Another place that you should call is L&L Tech, 520-669-5729. Talk to Lenard and tell him I sent you. He was the first to use the Stainless tower in the upper case and he holds the patent on it. Last I talked to him he was setting up a drive like yours with tower and XR gears for less than $3k. I have one of his drives but due to cylinder head issues my motor has not run with the new drive. I hope to have more feed back this summer.
At least give him a call and see what he has to say. He has taken very good care of me!!