I did mine at the same time as the injectors. I think the worst thing about just doing glow plugs (assuming they all come out OK) would be trying to get the passenger side valve cover off, it's a real PITA. The sucky part is getting the back lower bolts for the valve cover off. What worked best for me was going thru the wheel well with a small 1/4" drive ratchet for those couple of hard to get ones.
As long as you are getting in there, you'd be well advised to get a couple of those little plastic wedges from Ford that keep the UVC connectors from coming apart. UVC connectors coming partially apart have been a persistant cause of many threads around here. I'll see if I can locate a part # for those little plastic wedges and come back here with the info.
On edit: the Ford part #2C3Z-14A163-AB, that's right off the plastic bag they came in. I just noticed the instruction sheet is from International, that part # 1844193C91