What was the job that your relative do?
Prior to the Rev. War Valley Forge was actually a forge (called Mt Joy Forge) where iron smelted at the furnace was further refined.
Chester Co. is the loaction of many early furnaces during the time you mention.look at both furnaces and forges for the same jobs were used in both.Springtown forge,Coventry forge,Windsor forge, Warwick furnace,Isabella Furnace to name a few.Chester,Delaware, Montgomery and Berks are all very close to one another and workers often moved around.
the historical Society of Pa. in Philadelphia has a large archive of account books, etc. from many furnaces. Go to their web page and look at Collection # 212 for lists . the Pa. Archives at Harrisburg also have many records as does Hadgely Library in Delaware.
i might be able to help you firstname.lastname@example.org