A 510 engine will work. It doesn't matter which combine you get one out of,Super99 used one out of a 750. You have to strip the combine engine down to the block and head for the most part. You use the parts off the tractor engine to remake it to fit. The oil filter and cooler base has to be moved to the other side and the plumbing for the oil pump had to be changed to take the oil to the other side. You put a pipe plug and soft plug in where you take the combine filter base off. You use the tractor front engine cover,oil pan,water pump,front pulley,tappet cover,rear side cover,even the injector lines since the combine uses a cable and the tractor uses a rod. The combine lines aren't bent and spaced right for the rod to run down through them. The plate on the side of the injector pump has to be changed to hook the rod to vs the one for the cable.
Don't over think it,it's not a huge deal,you just have to swap things over until the combine engine looks like the tractor engine. I just don't know if it's worth the cost of overhauling a 354. You can buy a low hour combine engine for way less than it costs to overhaul one. Even better if you can buy the whole combine and sell it for scrap after you take the engine out.