Transmission questions

I have a complete 95 5.9fi motor and 518. I really want to keep the manual trans in my car. Is there a difference in bell housing size, ie. diameter between a 518, and a 143 tooth flywheel truck bell??? Why not just use the truck bell and flywheel, then make an adaptor for the 833, or other trans. So far in my reading, it seems everyone's hang up is with the bigger flywheel and bell. Can someone please help educate me as to why this isn't done? Thank you