I think you scored a Truckzilla chassis, depending upon which one it is, you may be able to run a 16/46 as a maximum gear. They were sold two ways, one was a .46 engine that was a real turd, the other was an extended chassis for the Savage. They were built by Hot Bodies. I had one and swapped it over to XL plates. My plates took a detour through Canada on their way to Florida.
Top to bottom, S-25; Truckzilla; XL...
I did a little frame work with my Dremel tool to get the mounts to move out a little more.
Until the XL came out, it was my favorite chassis to drive. Another reason I think it is a Truckzilla is those unique tires and wheels, they were part of the package.
Any of the Savage parts will interchange, except the rear drive shaft, from transmission to rear axle, it is an odd duck. Bud
[link=http://www.hotbodiesonline.com/truckzilla.html]Truckzilla![/link]
[link=http://www.hotbodiesonline.com/massive_tires.html]Tires and wheels! These will look familar...[/link]
Editing to add that those are Hot Bodies threaded shocks. I like them but the shafts bend easy. They are much heavier than a stock Savage shock, the shaft that is. Bud