Transfer case ?
 

Anyone know if I can put a top shift T-case into my truck that came with a forward shift? I realise I will have to make a block-off plate for the old hole and cut a new hole for the new shifter, but is there anything else I would need to do internally? I've never torn these apart so I'm not sure what the other differences are.

Going from a forwrd shift to a top shift should not require any modifications other the making a block off plate as you mentioned, if you were to got he other direction a new tranny would be needed. It should bolt right in, just be sure to take good measurements on where to drill the new hole in your tunnel. A 3" hole saw works very good for this.

You can also modify a fdw.shift case to be a top shifter:
- http://www.4x4wire.com/toyota/tech/topshifter/

Thanks guys. I have a line on a top shift case with low gears, figured I could swap it in for a while and keep my forward shift in case I decide to do duals. Sounds pretty straight forward.