I went the other direction and did an idi swap into an F150, it still needs some loose ends squared away but it's just about road ready. Things that come to mind that I had to do were motor mounts, gas engine mounts were riveted to the cross member, had to grind out the rivets. There's a hole in the cross member of the gas trucks that allows access to the oil filter, the holes not present on the F250 HD, maybe it's there on the 3/4 tons that came as gas jobs? I didn't have to change the cross member for the direction I went (diesel to gas). The truck I built originally had the 5.0, not sure where the 5.8 oil filter is positioned but could be an issue for you, it would suck to have to loosen motor mounts and jack the engine up just to change the oil.. I swapped the wiring harness, gauge cluster, battery tray, rad support, radiator and fuel system. I had good diesel tanks on my donor so I grabbed those, the lines and everything. Depending on the year of 5.8 you go with, think fuel injection, you'll need in-tank fuel pumps and all the related items. If you have a donor sitting next to it, then you should be good.. however, looking back, I wouldn't do it again. I just happened to have a trashed (badly rusted out) F250 diesel donor and a solid F150 gasser body with no motor in the yard. It's a lot of parts swapping and without the donor and my other factory F250 diesel to compare to I would have given up. Devil's in the details. I would say look for a running gas truck and use parts from your current rig if they're in good shape (interior, body), or find a good running diesel to throw in to your truck.. I have a 1987 6.9 in my 1990 F250 now, the $250 motor was too good to pass up when I found bad valve guides on the original engine.
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