[350TacoZilla]

Welcome to the forum and congrats on your new project!
Pretty much all common dana 60's are going to be 8lug but there are aftermarket spindle\hubs available to make them 6lug if you cannot live with 8lug, on the rear all the 72-87 14bolts are 8lug, there are SF versions and FF but in those years they are all 8lug. The IFS trucks had a heavy GVW 1500 and light GVW 2500 truck that was 6lug with the SF 14bolt but I wouldnt bother if you are doing a 60 front since rear would be weaker than front and a duramax would munch it pretty quick. You can also have the 14bolt FF turned down and drilled for 6 lug but really with the diesel in the plans I would just plan to go 8 lug all around and reinforce your frame. If you are able to get a parts silverado diesel I would use the rear from it since they are strong and have good disk brakes with a good parking brake (parking brakes are sometimes iffy on aftermarket disk brake conversions). If you end up with just motor and such then a 00+ silverado gas 2500 has the 14bolt FF with factory disks.