The book pays 25 hours for a valve job for that V8. That is what we usually do, including new guides. Occasionally there is need to remove the front cover to deal with the lower right side rail. This adds another12- 15 hours to the job.
Unless you have thread failure with the head bolt holes this should be a piece of cake. We usually take a week for the job, but this is only because we usually work it in stages, disassembly/estimating, parts gathering, head work, and reassembly. None of our techs that would do this job would take the alloted time. My main engine tech would like to do nothing but those heads. He probably would do two in a week if we had them and didn't have other things for him to do.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician