Re: e-350 coverted from gas to 7.3 non-turbo
To go further in depth, brakes don't go by engine size in larger/commercial vehicles, they go by weight, or GVWR. Not GCWR as trailers generally require their own brakes depending on the area you reside. Most brakes in a dually are the same with either the gas or diesel engine to simplify manufacturing cost. Brake calipers also must fit around the rotor without hitting the inside of any given wheel. Sometimes you can upgrade the brakes (both sides of an axle) to larger rotors, but the wheel clearance might not allow this.
The added weight of the diesel won't be more than yourself getting in and sitting in the drivers seat. The original V8 was knowingly a 7.4L block or something of similar size. Going with an N/A 7.3 is a valid aftermarket option in this case with minimal weight penalty. The weight of a turbo, additional plumbing to run it alone saves 50-80lbs right there.
In many cases hydraulic brakes are quite reliable, and to factor in something of similar weight, if you had an E350 upfitted with a dump body, and filled to maximum payload capacity, it would have to be driven in a similar manner as the RV, as the weight would be similar.
As for suspension, the added weight shouldn't do much to lower the performance/durability of the components. If you think the front end sits a bit low, and providing the E350 has torsion bars, you can crank them up. One full turn of the torsion bar bolt along the frame rail will result in approx 1/4" of lift.
Depending on the condition of the frame/underbody if you plan to tow a car/SUV you'll want to use a tow dolly with electric brakes. Some folks who have an RV and tow without a dolly generally have air brakes on the tow vehicle which allow more clamping force than hydraulic brakes, but are more susceptible to fade and has to be driven with caution.
When in doubt, a thorough inspection at an RV dealer will do the trick, although it will set you back a good $100.
'00 Durango R/T 360ci 290hp (modded); 138,500m
'06 Pontiac G6 GT 3.5L 220hp; 44,000m
'12 Chrysler 200 Limited 3.6L 283hp; 13,000m
'99 Taurus 3.0L 2V Vulcan 145hp; 154,300m - Traded
Amsoil in all vehicles!