Mini tubs and wheels

[68LSS1]

I've got a couple of questions I can't seem to find an answer for. Hopefully someone here can. I started off just planning on rebuilding my grenaded 350 and was just going to install a Dakota Digital Dash when the engine went back in. Now fast forward six months later--Dakota setup sitting in box collecting dust, truck down to the frame. But sitting on the K-member is a '98 LS1 and a 6 speed manual with it. This thing is really out of hand. Anyway, the questions: Anybody here run the Fatman Fabrications K-member? I'm looking at the stage III. Tubular A-arms, coil overs, and a Mustang II rack. Likes? Dislikes? Will I get any weight reduction over the stock peices? Now for the rear-end. I'm going with some coil overs here too that will give me a 4 1/2" drop. I don't want to put a 4 link in but would like to be able to run a 12-14" wide wheel. I'll be putting out 400-430hp and will throw on a 100hp shot of gas on top of that. I don't think with the rear suspension set up that wheel hop will be a problem but traction will. I'm putting the fuel tank in the back frame along with the battery and N20 bottle in the bed. It looks to me like if I installed mini tubs I could pick up almost 5" wheel space. I'll have to wait until I install the coil overs and remeasure as they might take some of this clearance away. Would a lot of positive offset be ok? Where would one normally try and put the wheel offset when doing a tubbed set up? As close to equal as possible? Or does it even matter (concerning wheel strength, handling, load/wear on axle bearing, etc)? I'd like to run a 10-12" wheel for everyday use and have another set for the track. And lastly, I already have converted to 5 lug set up a few years ago. The rear end is out of a early '70's truck. How much abuse can they take? Should I go ahead a get a 12bolt/9" setup going also? I know this is long--sorry--but any help will be greatly appreciated.
Brian