I have done some basic cleaning and upkeep on my 1960 C10 that had been sitting for an unknown number of years and got it to start up and run yesterday. It has the original 235 straight six motor. When I 1st got the truck home I found some loose parts under the valve cover. One of the rocker arm adjuster screws was loose under there and one of the valve spring retainers was gone. There was an extra head in the cab with all the valves and springs but no rocker arm assembly. I don't know why the head was in there but maybe the previous owner knew they needed a new head for parts or some other reason.

Things that I've done so far
replaced the points and serviced the distributor
rebuilt (single barrel Rochester B carb
cleaned out rocker arm assembly and replaced middle oil connector (old one was broken)
replaced valve spring retainer
new plugs
set timing (was pretty close but not perfect)
oil change
throttle linkage clean and spring replace (old spring was missing)
new fuel pump, filter, and hard line to carb

The engine will start and run but the valve that I replaced the keeper has some play. It and the spring can be moved by hand. I don't want to cause more damage by running the engine with this problem so I am looking for advice on what I should do next. I'd like to use the engine and now that I have verified it will run I am willing to put some money into getting it fixed up. I guess I should pull the head and see what's going on with that valve and address any other issues that become apparent. Is it a waste of time to just pull the head? If there are deeper issues I figure I need to pull the rest of the engine anyway (although I'd like to avoid that if it's not necessary).