It seems like it is now bracketed... between one day and one week!

It depends on how you are setup and a lot on what the customer really expects. Just get it swapped and running under its own power? Or cleaned up, serviced and ready for hopefully trouble free service?

Maybe best to think in stages. Pull the BB, clean, re-seal, service it. Clean up the tranny or not? Getting baked on grime off is a good 2 hours I think. Pull the SB + 904. Clean up the engine compartment and K frame. Even a quick job will be a couple hours with a pressure washer to help. Install BB and 727. Setup throttle and kick down, modify wiring ect. ect.

With a good shop + experience I think you are looking at several days minimum to do a decent but simple job. You need to price your time as you see fit... and make sure parts cost is accounted for.