the 68 RA1x had different Numbers for the carbs, dists, cams, and functional ram air parts, but the HP stayed the same. As far as HP, they still were the same motor. In 69, the HP Also changed between the 400, HO, and RAs motors.
Those are factory ratings, not real HP. But to your point, and to be honest, I don't think there is a lot of real HP difference between any of the D-port 400s (std, HO, RAI, or RAIII) by themselves. The difference is really the entire package. The 67 RA and 68 RAI were purpose built packages set up for the track with 3.90 gears, cammed and tuned for higher RPM performance. The 69 RAIII was really just the functional ram air scoop option added on to the 400HO. The small HP bump was probably more an attempt at marketing that option than a real HP difference.
