i'm familiar with a lot of buggy setups, 2.2 Turbo Ecotec, 4.3L, 5.7L, Saturn Transaxles, the whole nine yards. I've been up close and personal with rockcrawling rigs for the last 5 years, and I'm friends with a lot of the drivers.
Honestly, the most bang for your buck is the GM Shortstar engine. Lots of competitors are using it this year, it's an all aluminum block, extremely lightweight, packs a hell of a punch (around 200hp), and a slight bit smaller than the 2.5L. Here's a pic of one installed in a comp YJ.
Of course, you'll need to run D60's for axle strength.
Now, I know of a couple who are running setups similar to Jason Bunch from Tri-County Gear. What Jeffy forgot to mention is that Jason ran the D30 upfront with the Warn hub conversion, 37" tires, D44 in the rear, and finished in the top 3 for almost two years in a row. To me, this seems like the way a stock class rig should be built to limit breakage. I'm building mine very similar, actually.