Yea one day someone with there own lathe will make there own crank, mill and mod two engine blocks to fit together and have two pistons on one crank, a true twin piston motor, that day will be the start of twin cylinder power for nitro engines.A backyard [ so to speak ] job of this type would most likely see a twin straight line config design, reason being one piston being TDC and one being BDC is easier geometry to work out than a V config to get an even power output from both cylinders , alot of people would have heard a whiny motor that lacks compression on one or two cylinders, not getting the piston position correct in a V config will have that same whiny effect, uneven power through its power/torque curve. Its especially important to get this right, and is part of the reason we have not yet seen V nitro engines, expence of reaserch and design, anyways a back yard magyver, one day some where will do it some day, l have toyed with the idea, but lack a decent lathe and mill [ ppft like most ] hahaha, has stopped me...anyways the digger that does finnally do it will be a living ledgend in the eyes of some ! From there they will design a new manifold for a bigger carb to feed two inlets [ two cylinders ] and the same for exhaust.
Putting two nitro engines together now is less power than a picco .26 or .28.
Imagine a true twin stright or V config picco .26 , eye watering stuff.

That RB523 kit looks good too, never used them before but they look alright.