RE: fpe 5.8 with the shakes...
It all comes down to the crankshaft..Unless someone made a crank with a different stroke there's no way to make a Sachs 5.0 twin..Closest thing is a 4.8, made from two 2.4 Sachs cylinders...I have a Fox 4.8, and there are others out there..It is a very good twin if made by the right company, they are not all the same..I have a 4.8 made by A&M here somewhere...They made it with two different 2.4 cylinders..The crank is put together so loose that they drilled and pinned the parts, and when the owner crashed the plane the crank twisted and became unusable..Worst (almost) twin I ever saw..
I haven't run the Fox, but I don't anticitpate any crank problems..If Brison makes one I would trust that one also..Not so with Air Hobbies, do a search......There is another twin, made by Spehar using the Sachs 2.4 cylinders and a crank from Echo..Outstanding wormanship...Another uses the Horner case and crank..Good also....