You need to approach the problem differently, because simply spinning the same prop as a glow engine at the same RPM as a glow engine is not necessarily the most efficient way to go about powering an electric airplane. The only reason for needing a specific prop diameter and a specific RPM is lack of clearance for anything larger. A properly geared electric motor can actually spin a propeller that's more "scale" at a more scale RPM. Glow motors usually turn propellers that are much too small.

Glow engines waste up to half their power output whipping at the air for no apparent reason. That is, they spin the propellers much too fast to be efficient, which is okay because you can pack so much energy into a relatively small and light tank of fuel. With electrics, you need to make the most efficient use of the juice you have, because there isn't a whole lot of it to spare This often means relegating the 3-blade prop to static display only...

Your 4-engine plane may actually fly, and fly well, on much less Horsepower than four LA .25 engines. The problem is, we'd really need to know more about your plane than its wingspan and engine recommendation. Wing area, and an estimated all-up-weight with glow engines, radio, and fuel load would be a start.

Batteries would be the first thing to look at here. Roughly speaking, the power from 8 to 10 NiCd cells, with the appropriate motor and propeller, will fly a plane like a .25 glow engine. This is a general rule of thumb that really hasn't been properly documented anywhere, and the explanation of how it was determined is very long-winded... I'll save it for later.

Anyway, just estimating roughly, I'd say that because it's a big 4-engine plane, and not meant to do unlimited vertical, you can go with the low end, 8 cells. Each motor needs 8 cells, for a total of 32 cells in the plane. How you arrange that is up to you. You can do a separate 8 cell battery for each motor, two 16-cell batteries each running two motors, or combine all 32 cells into a single pack to run all four motors. If it were a smaller plane, you could even get away with using only 16, or even only 8 cells, depending on how you wire the motors. However, the currents required to power such a large plane far exceed the capacities of the batteries we have now, so I can't recommend less than 32 cells.

From there, you've got all sorts of options for motors. An easy, but expensive, option is four Jeti 30/3 brushless motors, direct drive to your 9x6 3-blade props. It's expensive because the motors are ~$120 each, and each one needs a separate ~$85 controller...