I have a 4l60e that was professionally rebuild about 25,000 miles ago. For reasons I won’t bother going into the trans was overheated several times and eventually lost reverse and 4th. The pan and magnet are full of clutch material. Everything in this transmission is new. A shift kit was installed at the time of overhaul. My question is this: Considering everything in the valve body and all internal hard parts are new, can I get away with just replacing steels, friction rings, and seals? Thanks for your help.
If no hard parts were overheated, like planetary pinions, that's basically what needs to be done to it. Next to cleaning the whole assembly, which makes it a full overhaul 
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You will likely need a new torque converter and everything will need to be inspected for damage and wear. Everything will also need to be cleaned. Just because the valvebody and hard parts are new doesnt mean they are good. Find the cause of failure instead of just throwing new frictions and steels in otherwise you will be throwing new frictions and steels in again in 5000 miles...