There are many different combo's out there. Ask around to some of the local pullers in your area and see what Classes they have. Your best bet would be to start out in a smaller class. A good combo that I have seen work around here is a 62/71/14 S300 turbo, ATS Manifold or similar, Blue Chip Redline Box, 200hp injectors, water-meth kit. You will defenatly want to Stud the head and possibly fire ring it. Valve springs would be a good bit of Insurance aswell. As for a double Disk clutch you will need to get atleast a 3850 or 4200. Anything less than that will not last long on the track. Is your truck a Cummins H.O. or Standard (6spd or 5spd). If it is a H.O. truck, you will want to swap the injector pump for a S.O. pump or a HRVP. The H.O pumps will limit your HP quite a bit. I have seen 100+hp gains just by going with a S.O. pump.
The turbo I mentioned is a 2.5 legal turbo. and it will still allow the truck to be a good daily driver. But if you get another truck to drive and make this one into a full time puller, I would give Chris at Empire Diesel a call and have him build you a S465. You can still drive it on the street, but it will be very laggy. The S465 is 2.6 legal and depending on who machine the inspection plugs at the pulls you go to, it may possibly be 2.5 legal.
If your truck is a 6spd with 3.54 gears, you don't need to change any gearing. Run 4th Low and a good set of 33" All Terrain Tires. Some places you go to may have a good high speed sled and a good track so you may be able to run 2nd high. Just be carful in 2nd high with the 6spd. I have seen many Main Shafts break in side the tranny, including my truck. If its a 5spd run 3rd low. If you have 4.10 gears with a 5spd, you may be able to run 2nd high aswell but it will have to be on a real high speed sled.
Hope this helps