The valve stem idea suggested by Larry worked great. I think it will work for anybody with a 123 or 126 plastic radiator. Here's what I did:
1. Obtain metal custom valve stem (i got mine at pep boys)..ensure it is the kind that has a metal nut and rubber washer. (Camel # 30-463 Worked for me)
2. Drill larger hole into area where overflow tube used to exit the radiator..be careful not to let plastic fragments fall inside. Make the hole carefully using smaller drillbits initially. Enlarge to diameter of valve stem
3. Obtain a piece of wire (I used a piece of 16 gauge conduit electrical wire but a coat hanger will do). Thread valve stem (with the air filling hole facing outside) - (minus the nut and outer washer. Leave the "inner" rubber washer at the base as this will be on the "inside" of the radiator and form a seal. Thread coathanger from overflow tube orifice out through the radiator top hose outlet. (You will feel the wire as it approaches the opening). Place valve stem assy onto wire and make a sharp bend in the wire so that valve stem assy will not fall off.
4. Pull wire out through orifice ensuring not to let go of other end (otherwise the valve stem might fall into radiator)
5. Using a knife or scissor, trim the remaining (outer) rubber washer so that it will sit flush against the outside opening (it comes with a slight lip/edge that needs to be trimmed). This washer will form an outer seal
6. Slip washer and nut onto wire and advance to overflow tube opening and fasten to valve stem assy. Secure
7. Remove wire
8. Attach rubber overflow tube to valve stem protruding from opening using existing hose clamp.
9. You're done!
Thanks to larry, I have managed to save replacing an otherwise good radiator!
