well...
It is kinda difficult to use a same car for track and daily drive (which i thought shouldn't be a problem : ) ) now my car, fitted with open pod filter, straight flow exhaust, full lock LSD, adjustable absorber, racing clutch and R888 tyre, it is stiff, noisy, slippery during raining and leg cramp during traffic jam, without all these! u cant compete in track; with all these fitted!is a torture to drive it in town (proven by me : ( !!!)
if u wanna compete with your skyline supra fren then go for a jap engine transplant, cos is cheaper, easier for sourcing and maintenance, although merc complete engine can stand extreme driving, but i guess u ll heartache... but i have to remind you that even though u put in RB26, in order for you to smoke your skyline friend, u need to pay double the mod cost cos too heavy, maybe u have to think abt HKS 2.8kit or 3.1kit, V-cam and a lot more goodies...
serious advice is, buy another car to play with them, the merc keep for daily use