I want to build a driver K10

[joeydurango]

Another vote for LS swapping one of your rigs. Did so on my '72 K10 and with a 2" lift, 33" BFGs, and 3.73 diff, and am getting 18-20mpg, can cruise at 75mph no problem, and way more HP than with the old 350. Advance Adapters makes an adapter for 4L60/80 to NP205. If you do all the work yourself and find a decent used engine it doesn't have to be any more expensive than what you're already planning. Not trying to talk you into it, it's just awfully nice...

Also, I second the notion that 33's on a 6" lift will look a little underwhelming. 33's fit on some stock trucks and look pretty good on 2", IMO. You might need 35's or even 37's, and then you can kiss your mileage goodbye!

Have fun regardless of what you decide, and post some dang photos!