Jim, the simplest answer is to look for a vintage Stanley #60 1/2. Here is an example (mods - necessary example only, and no affiliation): https://www.ebay.com/itm/Vintage-Sta...gAAOSwi8tbc33c
These have an adjustable mouth - and the advert must state this, otherwise move on. It should not have painted sides ... which can disguise the presence of cracks. The rear knob is likely to be engraved. Avoid planes that have labels instead as they are the new generation.
Regards from Perth
Derek