Before you go to all of that extra expense, have you tried just having a small loop bringing sap back thru the Sureflo pump? That is very effective for many who use the diaphragm pumps. It help just by keeping the diaphragm wet. While a diaphragm pump will move air, it does not move very much if the diaphragm is dry.
My only diaphragm pump is on my water heater. It draws water from about 14' of 1" tubing, then about 7' of 5/8" tubing. The tubing starts about 5' lower than the pump. At day's end I drain those tubings to keep them from freezing so to start it flowing the next time I am pumping with a dry diaphragm. I first open the supply tank valve, which has a water level higher than the pump so there is a head of pressure. Even with that the pump takes 45-60 seconds to pull the water to it, but as soon as the first water reaches the pump I get 3 gpm+ water flow.
My point is, just try a recirculation loop out of 3/16 tubing, and if your infeed is only a single 3/16 line add a valve in the recirculation loop to lessen the flow thru it. You only need enough to keep the diaphragm wet. If your infeed for the pump is a manifold bringing several lines in, you likely do not need a valve in the recirculate loop.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.