I found an M8 x 1.25 bolt that threads into the radiator bleed hole fine,
but nothing as short as the original.  I'll try another hardware store
tomorrow, but I'm wondering if anyone knows what's under the threads in the
radiator--can you just keep screwing a bolt down or will you break
something?

I know Alistair has cut or been there for the cutting apart of at least one
radiator (see
http://shufti.wordpress.com/2011/11/21/vanagon-radiator-replacement/ ),
just curious if anyone knows.

I had my radiator replaced at a shop, don't know what they used.  Here are
some pics from the bottom and top:

http://imgur.com/FxIsy,eE8qo#0
http://imgur.com/FxIsy,eE8qo#1

(In one you can see the point where the bolt started getting hard to turn
and it thought it would be better to stop and ask.)

mike