A couple of other variables to add to the equation:
I have 2.00:1 outdrives.
For every 2 inches in pitch, RPMs either increase or decrease by 300-400. For example: I went from 22p to 20p and my RPMs increased by about 500 RPMs. That put me into the recommended WOT range of 48-5200 RPMs @ 5000.
If I went from 22p to the 26p that was on the chart, that increase of 4 inches of pitch would drop my RPMs by about approximately 800 RPMs. So from the original RPM of 4500 minus 800...well that puts my waay below the range.
I assume you bought new outdrives also when you repowered with the 383s, in hindsight is the 2.00:1 drive correct for these engines or do you think the 2.20:1 would be better ? It's my understanding that 4 blade props create more drag, certainly with the B3 setup it's even more pronounced.