Good to hear from you Bruce!!!
You can install Banshee trans into RZ350 engine. First 3 gears have closer spread while top 3 gears have bigger spread. Will need to increase sprocket-ratios to get same top-gear. There's even guy in Europe making custom-gears in any ratios you want. Should use RZ shift-drum and forks, seems to operate a little slicker. Pro-Mod trans shift best with undercut dogs. Some
Banshee transmissions for sale.
Great idea on 450 engine. There's talk of using Honda 450 engine too.