To answer your question about lifting, the 67-72 trucks and 69-72 K5's are very easy to lift. Generally a 4" lift of either does not require driveshaft modifications, but I did have to add a CV joint to my 69 when I initially did a 4" lift. You will want to add a steering correction. For the 67-69 years the front axle is a closed knuckle Dana 44 which requires a adjustable drag link to adjust steering. The dropped steering arm that is available will not work on the 67-69 closed knuckle axle.
Rear axle can be lifted with springs, blocks, or a shackle flip. Depending on how high you want to go, some use a shackle flip and block or shackle flip and spring to get to the desired height.
You will need to modify your brake lines slightly when lifting. You might have to modify your exhaust slightly, depending on how it was designed. When I lifted my 69, the tailpipe ended up hitting the rear spring hanger.
I bought all my lift stuff from a supplier that is involved here, Off Road Design and was very impressed with their prices and their knowledge.
$1,500 for a no rust first gen is a bargain - get it before it gets away!
