Easiest and cheapest option is to go 6 speed with No DCCD. You can retain the rear diff you got now and just drop in the right ratio (usually 3.9) crown wheel and pinion in the diff. If you decide to replace the diff, you dont have to go up to the larger R180 so dont get talked in to it if you dont really need it as it'll cost you more dollars as you'll also need to upgrade the entire rear end (driveshaft, hubs, brakes etc)

This conversion could cost you as little as $5000, upto $10k depending on what options you pick.

If you got any questions drop me a PM.

And while the box is out, also suggest replacing the clutch plate, cheap job to do if your clutch is even slightly showing signs of wear.