The stock '74 915 transmission was functioning fine, but was open diff, had the weaker 7:31 ring and pinion, and none of the updates later 915's got. So I sourced a euro 915/67 transmission from the '80's with the stronger 8:31 R&P and aluminum side cover, factory LSD, and most importantly external oil cooler. This transmission should work well with the 3.6. All the extra torque the 3.6 makes should work well with the stock ratios as well.
Here are a couple of (not great) pics of the transmission bolted to the old 2.7 for the trip up to Al's shop.
