I really don't know. As far as the math goes, you need less of a BS. Would I still need a 2" BS?
14.640 - 13.50 = 1.14
13.690 - 12.50 = 1.19
Looking at the Mudb8's chart. it seems like the rear shock might be to short?
Sorry for the stupid questions, i'm just having a hard time wrapping my head around this.
they're not stupid questions at all. and yes, the math looks fine. I'd round up to the nearest 0.5" for good measure.
Therefore, you know you'll need around 1.5" bumpstop extension. Well, you can put together 1.25" or 1.5" from one of the expensive fancy bumpstop extension kits out there, or you can just make your own for a whole lot cheaper.
For example, you can buy 2" tall body lift pucks from Performance Accessories and cut them down to 1.5" (or whatever you need). "Mini" blocks fit in the rear, and "Big" blocks fit on the front spring pad, and they run really cheap on ebay/amazon/direct, etc.
Another example is buying some raw bar stock...like aluminum, delrin or UHMWPE. 2" diameter is what fits in the rear, and 3" diameter fits on the spring pad in front. Cut it to fit, drill a hole through the middle and bolt it up.
Ok, so here's how I think about it. Stock is roughly ~4" uptravel/~4" downtravel in front. Anything over that is an improvement.
So take lift height (3"), divide by two (1.5"), and use that as a starting point for bumpstops and choosing shocks. 2" lift, 1" extension, 4" lift / 2" extension, etc. Now, try to pick a shock that gives you a 50/50 to 60/40 travel ratio around that. So you know 1.5" bumpstop extension with a 3" lift gain over stock gives you 1.5" additional uptravel over stock...so call it ~5.5" uptravel total. That means you want a shock around 10" travel, for ~5" up and ~5" down. You also know the stock compressed shock length ~13.50" or so, 13.50" + 1.5" = 15". So the max compressed shock length you can run with 1.5" bumpstop extension is 15". So look for a shock length at 15" or slightly under, with ~10" travel. And that's what you've done...14.6" compressed length is appropriate.
You can apply the same logic to the rear, but things get funky really quick. Pinion angle rotation changes things a bunch, and the bumpstops don't line up right...so you can end up needing different extension than your math might suggest. No big deal, just buy plenty extra and adjust it on the rig as you install everything and check full bump for clearance issues.
All of this is just theoretical starting points, and of course there are tire size clearance issues and suspension interference issues to consider as well. The above just describes addressing the shocks...you still need to figure out the rest...which may add additional bumpstop extension requirements.