I have a R34 GT-R front bumper and HKS Kansai C/F Hood on my R34 GT-t.
Assuming you have a GT-R hood, the R34 front bumper does fit with no mods as long as you get the upper grill support brackets that bolt to the headlights as well as the cross bar that the top of the bumper attaches to. The stock GT-t bumper re-enforce will work with some slight trimming I believe. I opted for a GT-R bumper re-enforce (light weight allumi) so it fit like a champ.
As far as the attaching the bumper to the fenders, only one bolt hole will line up so you can either toss the plastic re-enforcement piece that the front bolt goes through and use rear bolt to hold the bumper on each side or re-drill the forward hole in the bumper to the correct position. I used the rear bolt only as I was too lazy that day to re-drill the bumper. You will end up with the tips of the bumper about 4mm past the end of the fender wheel arch, but it is not too bad. There will also be a small gap between the headlights and the bumper at the corners, but in all it looks tits hot!
As for the hood you need to buy GT-R hinges and a GT-R hood latch support to make it work. If you get an HKS Kansai hood you can "mod" your GT-t hinges to make them work but you need a butt load of washers to bring the hood up to the correct height in the back. You will need to drill a new hole in the GT-R hood latch support to bolt it to your lower radiator support frame on the car but it is a piece of cake.
I will try to get some photos of my setup for you guys if you want.
If you have any questions feel free to PM me I will be happy to help you out.