Diesel Bombers - transmission and clutch help

the 6spd you have should be good, depending on power levers you might want to upgrade some parts in it but should be good enough for whatever you put on it for your application (daily street driving and towing, as stated above). If it was an all out race truck or pulling truck then a modded trans would be more of a need, but not for anything like you want...

As for the clutch that is fully dependant on you current power and power goals for the truck so your not buying more clutch then you need but also are not buying 2 different clutches. It also depends on the weight and how often you tow at those power levels.

For example, my power goals are just about 500HP, and I regularly drive the truck on the street, and tow a trailer that is more than 10K at least once a month during the 3/4 of the year. My choice was to go with a small street rated dual disk (SBC SDD3250-GK), now I just need to get it installed, lol...

Here is a quote I have frome when I was asking about what I needed for my truck on a different forum...
"you'll be at the VERY limit of a single disk, 475 HP and 900 TQ is about the limit. You'll want to go with the double disk in that case, as let's face it, you're gonna want more power down the road. Here's what I'd be looking at in that case, SDD3250-GK (G56). This is good for 550 - 625 HP and is a 3250 lb pressure plate. Not a huge increase in pedal pressure, doesn't NEED the upgraded hydros, but I would HIGHLY recommend them. Beyond 500 HP and you're gonna want to look at a billet input shaft."

I hope that helps...