If you buy Motor mounts for the SD to Cummins conversion you will not need to weld them. If you make them yourself you will. I used GOS singles for mine I have heard others use fordcummins mounts and have been happy enough with them. I know with the Autoworld and GOS and maybe the destroked (they might all be the same maker, I don't know) Mounts you will need to drill some holes in the cross member, it is easy when there is no motor in there. If I remember right the fordcummins mounts you do not need to drill any holes. If you do get the GOS mounts remember the longer mount goes on the turbo/passenger side of the motor. It can be hard trying to picture how all this will go together without tearing into it and having the parts in hand but when you get in there and you have all your parts it makes a lot more sense.
Are you planning to use the Cummins fan or go with an electric. If you plan on doing any towing I suggest the factory fan. you will need to make sure the motor sits far enough back to clear everything. also you might need to redesign your fan shroud I know my 6.0 shroud works fine but I don't know what the 6.8l shroud will do.
Also what are your plans for brakes? hydroboost or rig up a vacuum pump? You might start to look into that too so you can get your parts lined up.
Are you planning to use the Cummins fan or go with an electric. If you plan on doing any towing I suggest the factory fan. you will need to make sure the motor sits far enough back to clear everything. also you might need to redesign your fan shroud I know my 6.0 shroud works fine but I don't know what the 6.8l shroud will do.
Also what are your plans for brakes? hydroboost or rig up a vacuum pump? You might start to look into that too so you can get your parts lined up.
