Cummins swap/440

I did this conversion on my 86 D350 dually and it's a mixed bag. At this point, with 60K on the conversion over the last 7 years, I'm still neutral. I use my truck to haul around a track car and to pick up building supplies. If I drove my truck a 100K per year and or towed/hauled 10K at a time I'd be way more pro cummins. Gas mileage with 440 was 7mpg almost no matter how I drove it. I typically get 19 with the cummins empty and it drops to 17.5 while towing my car. Oil change and filter on the 440 was about $20 for materials, it's like $50 with the cummins(3.5 gal per change). Fuel pump replacement on the road $30 and available in any town, $1200 for the diesel injection pump before labor and few small towns have anyone with the expertise to do it so add a tow bill on top of that. The truck is noiser with the diesel because I did no additional sound deadening since my interior was already done and I did not want to tear it apart. I like the turbo cummins much more on the highway but dislike it around town as mileage drops to about 13 stoplight to stoplight. The 440 hardly changed in town vs. hwy. My main reason for doing it was I'd worn out the 440 and was faced with the cost of another engine anyway, and like you I bought my cummins used. I'd be less than neutral if I had had to modify my firewall as many do for the hydraulic clutch. If you can find an 87-88 /6 OD truck you can use that bolt on hydraulic clutch bracket and save a ton of time/cost if yours is a manual. Given how I use my truck I don't think I'd do it again, especially if my gas motor was good. And that's really the key (the few miles I drive it), unless of course you just want to and have the time. Just my opinion though.