I know t hat no matter what size one builds, they can always be just a bit bigger
!/5 is a nice scale, and there are retracts available in that size. I'm not too sure what gear would be available for a 110" Hellcat. For my protptype I mortgaged the farm and got a beautiful set of Darrell's gear over at Sierra. Spendy, but what a piece of machinery! They are absolute georgeous!
Also, having another 'Cat in 1/5 makes it possible to mix and match parts. I'll bet most of the glass parts could be used on either model.