Hard to answer directly since there are a few other factors that determine driveline length.
In general though, you will still need a long-slip front shaft if your front shackles are still in the OEM rear configuration and you have a decent amount of flex. If you have time, I'd build the triples first and then do your measurements for shaft lengths to make sure you get them the length they need to be. Rear shaft may need a double-cardan at the case if you have lots of rear flex, and you'll need to account for shaft compression on that end just as you account for extension on the front (not nearly as much though, but depends on how long your rear leaf springs are).
For me, I did a full flat belly along with an R10 adapter on my 85 Xcab and my shafts turned out being almost the same length. Only catch is that, as mentioned, the front requires more slip than the rear. However, it's still nice being able to carry a single spare square driveshaft that fits either end. Don't recall the actual length, but mine are somewhere in the mid 40" range each.
