GD-600 for Gear Reduction for King Hauler

[Heavy Metal]

Will be putting a GD-600 3.8:1 GRU on my King Hauler. I've seen GRU's mounted 3 different ways so I'm asking for some pro's and cons on mounting options from those that have been there, done that.

1. Between motor and tranny.
Pros: solid mount, minimal added backlash, less wear on tranny with reduced input speed
Cons: requires modification to tranny mounting and maybe other mods, I think I read the GD-600 shaft has to be turned or filed down?

2. Direct mount to tranny output.
Pros: solid, minimal added backlash. minimal or no mods to mounts or chassis
Cons: ?

3. Mount to chassis halfway down the drive train between tranny output and diff with cups on in/out shafts for short drive shafts each side.
Pros: seems easiest option, less mods
Cons: most additional backlash of 3 options?

Other options?

Until I get my hands on the thing I have no idea what has to be done to mate these in/out shafts or attach cups. Posts I've read have not been specific on this so tips/suggestions welcome there as well. I'm a newbie so very few spare parts for this sort of thing in my shop (yet)

Also, has anyone run across spec tables online that show the length of the different model Tamiya (or other manuf.) drive shafts? Would my local hobby shop be able to look this up?

Thanks.

Joe