Remove valve covers, rockers, pushrods. Put 1/2" wooden dowel rods into each lifter (chamfer and split with a hack saw the end, drive in with a mallet so they hold securely), lift, and clothespin to hold the lifters up. Remove 2 bolts, cam retainer, camshaft with gear on it. Remove injection pump gear, pump, vacuum/ps pump from gear case. Replace gear case, putting timing pin housing on new case, aligned for TDC.
Not a job for the learner or faint at heart. Also you need a new dowel pin to help align the gear case. Cummins #3900257.
Use RTV sealer for gear case to oil pan. The new pink gear case to block gasket 3938156 goes on dry.