You seem to have a decent rough outline, great! /forums/images/graemlins/thumb.gif
I am not familiar with the holleysystemx setup. /forums/images/graemlins/dunno.gif 425HP and 425ft lbs of torque is a lot for a 350. That will be a fairly healthy motor that will make power higher in the power band because of the camshaft it will take to make that kind of power. You could build it with AFR heads, multi port injection, and a really good performance cam made for lower end power. That would be a better combo but expensive to build. I would consider stroking the 350 to a 383 with a slightly milder cam around 450-480" lift and a good head like a merlin torquer, Pro 1 topline, or even vortecs with an overall compression of around 9.1:1 to 9.5:1. Closer to 10.1:1 if you go with aluminum heads. I am not a big fan of compression though, I have had a bad experience with pinging in my 406 at 9.2:1 on 91 octane, with wonderfull hi performance cali gas though. /forums/images/graemlins/mad.gif
i would aim for more like 300-350HP and 400 ft lbs with a flat powerband instead of 425/425 because...
1. The price of gas that is probably not going to decrease.
2.A 425/425 350 is pretty healthy and will probably struggle in the lower RPM range because of the cam required.
3. You only plan on running 35's at the most. 300HP can man handle 35" boggers no problem.
For the tranny you don't list what your K5 has stock. I will asumme that it is a TH700R4 auto because the majority had them. Unless you are dead set on running a manual I would consider just running your current th700 with a good shift kit & cooler and see how long it lasts, especially if it's in good shape currently. Then you could have a custom th700R4 built up to handle 350-400HP and 35's without a sweat for probably not much more than the cost of your average NV4500. If the NV4500 needs syncros, clutch, gaskets....you will probably easily exceed the cost of a built th700. Plus, in mud an auto is the way to go. /forums/images/graemlins/thumb.gif
I would forget about the atlas Tcase unless you are dead set on it. The stock NP208 rebuilt is adequaet and finding a 241 at the junk yard would be cheap and a good upgrade.
A 6" lift would be nice with a set of 35" boggers or TSL's unless you plan on running wide rims, than I would consider an 8" kit. BDS or Tuff Country is the only way to go! You will need a pair of custom shafts, I would recommend the stock shaft just lengthened with a sealed slip up front with a 1350 joint new shaft at the rear. With only 6" you probably don't need a CV, I don't.
I would go with a 3/4ton set. a 14BFF and 10B with 8 lug outers would be perfect and swap directly in. A 3/4 14BFF is a DIRECT bolt in, a 1 ton 14BFF is NOT a direct bolt in(the spring perches are narrower on them and the shock mounts are opposite). A 3/4 10B will also be a DIRECT bolt in but a 3/4 D44 won't, it will take smaller brake lines up front but IIRC you could just use your 10B calipers because I think they interchange between a D44 and 10B.
4.56 gears would be nice with 35's and they come factory in some 3/4 ton running gear but can be hard to find because most trucks came with 4.10's and even 3.73's.
35x16" boggers are a great tire for what you want to do and I love mine! Go with the 35x16, not the 35x14.50 because it's a smaller tire and has the same tread depth as the 33" tire. The 16" wide bogger has deeper tread and larger side lugs, it's a smaller 39.5x18 IMHO. If you plan on spending 50% of the time on road and the other 50% off, switching tires and wheels will get really tiring IMHO. I would go with a tire like the 35x14.50 SSR or 36" TSL radial. Both tires are excellent offroad while still retaining decent road manners with minimal noise and decent tread wear. I can attest to the SSR, I loved mine on and offroad. /forums/images/graemlins/waytogo.gif
Your plans seem to be similar to my K5 so here is some pics.
