If it isn't the same as that gtr cluster page I sent you ages ago, you could just swap the speed sender over from the old one onto the new and fit that into the old cluster housing.
There is a writeup in the tute subforum a couple of years ago on how to do it.
Hubs are different material, shock mounts are different, but I didn't think the track is wider.. Guards are, but mine is the same as a gtst, all steel front as well. So same drivetrain as a gtr with more weight and less tyre.. awesome.
Interesting is that part number comes up as s15 rear wheel bearing.
*edit
bubba - have a read of this thread, http://www.skylinesaustralia.com/forums/topic/37813-r32-headlight-questions/page__hl__gtr+headlight+clip__st__40
There are some brackets you can buy to clip the gtr grill in to.. they simulate the gtr lights with the inbuilt clips. The part numbers are on here (sau) somewhere, remember it from years ago. Otherwise gtr lights are not exactly rare..
Leave the sub there and take the control module out? What more do you want? At least it has a fault light so you can do some diagnosis, rather than guessing..
Serious though, maybe an inspection mirror will let you see it, unless you have enclosed the lot.
When you do have the light lit, leave the ingition on and open the boot. Look on the underside of the parcel shelf and the left hand module has a led indicator in a see-through port on the bottom. Count off the flashing sequence and look in the manual for the fault code relevant.
Went through this myself recently, even bought a secondhand box and was going to fit it and play the odds. Unfortunately it wasn't quite what was advertised, so decided against it after research.
The options I ended up with were rebuilding (competition gearboxes) or buying a decent one. Ended up finding a brand new ser3 r33 box for not much more than a rebuild. Within my budget as well.
The extra expense of rebuilding the earlier boxes is there are a few parts that are not available anymore, and you have to upgrade internals to the same as the one I bought anyway.
I fitted my own internal 044, used a e-series falcon sock. Had to machine the fitting for the sock, hardly impossible, just a pain. If you can get someone to do it real cheap, or get the right fittings, then go for it.
Even when I had 235/45/17's all around, with the new ones on the front and worn ones on the back it was enough of a difference to produce this effect.
What rims and tyres are you running currently?
No, currently have an old r32 spec 5 speed totally missing 3rd-4th synchro, with the gts4 4.375:1 diff ratios front and rear.
Have a brand new ser3 r33 box waiting to go in on monday so will finally get to experience what everyone else takes for granted (my gearbox was on its last legs when I bought it over 4 years ago).
I can't think of any reason why you would want to fit the 6 speed instead. 5th is the same as 4th in the 5 speed (ie 1:1), and the overdrive is about the same so you don't gain longer legs for distance driving. Just have to shift more often.
A bit better search revealed:
getrag ratios
1st 3.827
2nd 2.360
3rd 1.685
4th 1.312
5th 1.000
6th 0.793
r32/33
1st 3.214
2nd 1.925
3rd 1.302
4th 1.000
5th 0.752
Knock everything into a gearing calculator like this one http://www.boosttown.com/gearbox_differential/speed_calculator.php and see what you get. The getrag with 4.11's is shorter than the 5 speed with 4.375's.
Fitting a getrag was a fleeting thought, but the hassle and extra expense to end up with something that is a curiousity was not justified.