The 60 degree Evinrude v4's you have on right now are super light weight. I would assume they are 25inch shafts for a boat that size and style of the hull from Striper. Those engines are roughly 320 lbs each. So it's safe to consider if you go single plus a auxiliary engine, you will have to go 30inch shaft on the main.
250 ETEC G1 520 lbs
Yamaha 250 560 lbs
Verado 250 600 lbs plus all the crap that comes with the machine ( like the steering system that draws 5 to 15 amps of power continuously, and the rigging is crazy expensive )
Suzuki 250 600lbs
None of these weight specs are for 30inch. There is added weight for that little extra shaft, adapters and or lengthened exhaust housing and steering shaft.
Auxillary options will be 120 lbs for the newest Tohatsu 9.9 - 20 hp in extra long shaft remote models with power trim tilt option.
Twin 115 four strokes they are all right in the 390 lb range per engine. Which puts you in the 780lb range on the back.
Tohatsu just came out with their new 115 Four stroke which is pretty awesome I must say. Sips gas and extremely quiet. However same thing 390 lbs
Hope this help you a bit. Feel free to pm me, and maybe you can stop by the outboard mecca land