Nice pic's . . . you've done well.
You could just change the .8M gears if you want but there's a bunch of other front end stuff that changed - I doubt you could just install the upper deck, and servo mount.
Remember the EVO front bulkheads are closer together, there's now a steering post, the one-way is narrower etc. etc.
In fact, with the EVO conversion kit, pretty much everything is new/different forward of the rear suspension and 2-speed assembly.