I did it so it's possible but probably not optimal. My original brass plug was completely bodged and leaking. When trying to weld it out I found out that it wasn't steel... It does however contain a magnet that's cast into it. The tread is the same as the filler plug in the top but I think the drain plug is "conical" and the filler plug isn't. So mine is still leaking a little.
Item looks more like a filler plug, as drains usually have a magnet. The line drawings in two stroke manuals I have suggest a magnet on them. I'd post a pic of later drain plug, but photobucket is a pain at the moment. Here is a link for assistance.. http://www.uksaabs.co.uk/UKS/viewtopic.php?f=12&t=179840
Topic 
Gearbox drain plug
Posted - 27 Jun 2017 : 08:01:08 
