I've attached a photo of what I did.  Hope this clear!  1) Remove the fill-tube collar from a Heritage; 2) Drill holes in the Tradition Em-Tor so that they match the location of the screw holes on the fill-tube collar.  Then you should just be able to screw the collar into place.  I also put a bead of silicone caulk around the edge to try and make it a little more air tight.  This set up will allow you to use the early G Series fill tube and bag adapter.  You can then use the HEPA bags on your Tradition! 

Here's a photo with a HEPA bag.   I installed an F-Style bag adapter, but you can certainly use the older style too.   Sorry for the size of the photos.  I just got a new MacBook Pro a couple of weeks ago, and I don't think iPhoto will let you re-size photographs.  Guess I'm going to need to buy an upgrade to do that!

You can buy a Heritage fill-tube collar from a007kirbyman.  They're probably $10 or $15.

I've been lucky enough to find things like Tradition Em-Tors at vacuum shops.  I've found a couple of shops that have old cast-offs in back rooms.  I wonder too if you hit a Kirby Distributor at just the right time that you can find what you need.  They take them in trade, so timing may be everything!