with 79 axles and a 3 speed t-case you have different patterns at the t-case and axles. you have several options:
-change out diff flanges or redrill if round type (stock ones on a 79 were square and no room to redrill) and then use 67 driveshafts and just have shortened or lengthened to fit your t-case placement and lift.
-change out the park brake drum on rear of the t-case and ront output flange to 79 pattern and use 79 drivelines and have length changed to fit your needs.
-as mentioned above, have custom drivelines built with langes you have now on the t-case and diffs. If you do this, I think you will spend more money and find it harder to come by spares. If you keep each driveline with same flange pattern or each end then you just have to worry about length and balance.
Its my opinion that the later drivelines, flanges, u-joints, and retaining bolts are stronger. The u-joints are bigger and the bolts are bigger at 11mm. Yes, a strange size but bigger none the less.
I had a similar situation and opted to make the rear shat all 79 type and the front shaft all 67 type. This required buying one diff flange for the front diff, a park brake drum for the rear, and a used 79 driveshaft. Then having a local driveline shop retube the stock drivelines and balance them. for front and rear this was about $180 in driveline work and about $40 for the driveline flange (new) and $20 for the park brake drum (used) and $40 for the used 79 driveline.
Expect to pay about $300 each for custom driveshafts.