Do it!!!! Twin I beam suspensions handle well on road and off road the tire contact patch stays level with the surface its on to a certain degree. It wont be easy. Your biggest mods will be fabricating 2 crossmembers one for the i beams up front(their pivoting mounts overlap each other) and one to support the transmission. Aside from that re-use the coil buckets with integrated shock mount(some have twin shocks and these buckets can be bought). The radius arms mounts will also be fabricated easily or simply re-used(this would be a good time for longer radius arms it allows for more axle droop while flexed. The steering shouldnt be too bad to fab. Motor mounts are simple. Although like on guy said its a long motor and I have heard of a 300 in a xj before and it required firewall modification.
Also the bronco should have a 9 inch rear and those need no explanation of their benefits. With the front being a dana 44 it is pretty stout aswell (even though it ifs design is slightly weaker. F250 springs can be lift coils for broncos. Set up ideally for suspension flexability this will be a pretty tall rig.
has alot of i beam parts and will be a good source of lift info and overall design capability.
Yes this is alot of work but the 300 is a torque monster and with a offy intake,4bbl carb, cam, and headers you can add over 100 hp. The transmission if your lucky is the granny gear new process 435 or the ford t18 both very desireable 4 speeds in the cj community. Not sure of the transfer case though im sure its stout. It will be drivers side drop.
Also the desert racing people may have some info on swaps like this. This could be one very unique and very capable rig that will bring you alot of respect if done well.
Good luck. I hope to hear more on this build.