Wanting to get a 450 or 550 Chassis Cab, what motor?

[31 YNOT]

My dad and I are looking into upgrading our farm truck (5.4L F-250) to 450 or 550 with a nice flat bed for hauling seed pallets and so it has more hauling capacity for our goose neck and liquid trailer. He has me looking for trucks, but I am not sure what motor I want to get in the truck. 7.3, 6.0, or 6.4.

We need something that is going to be reliable and start when ever we need it. It wont be driven daily so it will have to be able to handle sitting around for periods of time.

What I know about the trucks and questions about each-
7.3L
-Good reliable power plant
-We need a 4x4 and I know the early SD trucks had a weaker front axle did this include the 450/550 trucks?
-What types of problems do the 7.3's have

6.0L
-05-07 can be a good reliable motor
-I am guessing it would be wise to put head studs and egr delete, how much would something like this run me?
-Is there anything else I need to watch out with these
-Coli front suspension so it has a better ride than the 7.3

6.4L
-Horrible fuel milage stock, but I think I would delete everything to help with that and make it run better
-How much is deleting everything going to cost me, including egr and waste gate since we will be towing a good amount of weight
-Can I delete everything on a chassis cab just like the regular trucks?
-Can make huge power with just tunes and deletes and run great


So which ones should I be looking at? I try to do a lot of reading on here but still dont know. How much money should I be looking to spend on each motor to make a really good truck out of it.

[JLDickmon]

F650 with the Cummins ISB..

[31 YNOT]

We thought about that, but the truck wont fit in the smaller shed where we keep it, we would like something a bit shorter(length wise) so it is easier to move around, and a 4x4.