I didn't install a 4 into 1 believing there was a power advantage, but rather because the physical layout seemed to offer potential for cooling drag reduction. In fairness, it is not the only layout with potential, but the scheme fitted the -8 very well.
When delivered a few years ago my AWI pipe was a little too deep in the belly, ie too close to the bottom panel of the lower cowl. I think it was early in the game for them. Made measurements and sent it back for minor changes, which were done quickly and cheerfully. Good guys.