1995 3500 dually rear wheel conversion

whats going on everybody i am very new to this website, this is auctually my first thread on here... but anyway i just picked up a single cab 1995 3500 12 valve dually with a utility body on it the truck has 98k and no rust on the cab corners, doors, fenders but the under body has the typical suraface rust not rotting or deterioration. but the best part of this is i got it for free... dident pay a penny. i was looking to do a rear wheel conversion and remove the dually and makking it a single wheel but i have a couple of questions about it and am very curious how this is going to work and what i need. i was hoping to put an 8 foot bed on it bud im not sure if that would work or not or if i would only be able to put a 6 foot bed. but i did some reaserch never really got any good enough answers. but what i really need to know is how to do the conversion people have been telling me al you habve to do for the front is take out the front hub spacers and put new rims on it witch dosent seem hard at all, but with the rear i dont know if i can do the same and keep the axle thats on there or am i going to have to do a whole entire swap of the rear end. any information on how to do this would be very helpful this is my first cummins i recently had a 7.3 powerstroke but im only 17 and really looking to do this conversion and any help will be every appreicaated