Picked up my 19' omega a few months back.had stock 350 sbc.with berk jc-a pump.turned it 4200 rpm. ( no gps #'s)Went Craigslist shopping and added: ebrock performer rpm alum heads,aed 750 Holley,ebrock performer rpm intake,1.5 roller rockers,comp 276 roller cam setup,electronic ign. running logs and snails.( want to keep the engine covered). Now I'm getting 55.5 on gps but tach maxes out after 5000rpm and bounces around so no rpm readings until new tach. Recently picked up 383 short block should be done in a week or so. So assuming 450+hp trying to estimate speed? Will add diverter and pump work. Talked with jp marine. Joe recommends b/c impeller,inducer? And rebuild. What else should I do? Looking to get 70mph. Without squeezin'(nitrous).

If this is an all out effort deal, I'd put the 383 in and see where its at as far as speed, then trim the impeller to the motor, and see'in what it wants. You may end up with a B/C cut, but thats along way from an A or A/B cut. once its cut, you can't put it back.
I'm runnin an A cut on a 350 @ 4600 rpm & 55 mph, and another 100-125 hp would prolly get me 4-500 rpm.
Sounds like the pump is worn, and a refresh would lower your rpm on the 350. mine lost 3-400 r's with the fresh pump,  loader and rideplate were added too.
As far as rpm Vs. mph, every boat is different, and underwater hardware setup is important. Sounds like in the 65+ mph area.

Daniel

Is your 350 stock? I thought a pump needing a rebuild would turn higher rpm?( cavitation).

When I had an Eliminator I wanted to keep the engine covered as well. When I bought headers that would fit under to let the engine breath I got a considerable jump in rpm and speed. Logs restrict the air flow, if you want the rest of what you doing to reach its potential you gotta let the engine breath.