Hahaha, +1
IMO, The c34 for towing. Also the ease of finding replacement parts, since they share so much in common with the Skylines. This makes repairs/mods more cost effective. The c34 is still a very comfortable car upto 6"2' drivers height with sunroof's (If I was any taller I wouldnt fit into my car), thats if you want sunroof's.
As for the front end conversion...
Check the last link on the first post for a rough price... here this is just the ccubed version (all fibre glass) and I think it is minus paint and fitment.
If you want to go down the Genuine r34 GTR parts route, the only fibre glass you will be using is the conversion fenders, which you can get from ccubed (pretty sure they used Darrins masa guards to make their moulds). then open your wallet for OEM bonett, frontbar, rad support (which you will use only half of), bonett latch and stay, headlights, front indicators and side indicators. then pay for fitment (unless you do it yourself, but be warned you have to shave 15 - 20 mm off the front skirts once you get the radiator support off your car). Then paint you will have to blend the front doors. No doubt while your there you will want to put on a front mount (because the front of the gtr bar looks silly without one), and make up heaps of little brackets to mount everything in the normal position (thermo, bonett lock support and auto trans cooler)... your 5G budget can quite quickly disapear....