Check out conversion perversion on this website
http://www.shoptalkforums.com/index.php
Direct link to the conversion pervesion section:
http://www.shoptalkforums.com/viewforum.php?f=19
There are many many threads on there about putting Mazda lumps into aircooled VWs
Even though your not putting too much surprise torque into the tranny, make sure the current one is up to scratch. You are right though. a well built VW transmission will take the power as long as your not mean to it - unlike the subaru version which can chew up the tranny quite quickly.
Can't remember 100% but I think a company called rhino were doing some competitvely priced stock-ish transmissions for just this type of thing.
Also Adaptor plates are available.
Don't think you will need a true cradle as the rotary is so light. You can get extra support brackets though (again available almost off the shelf or drawings for home creation) for the tranny again look on Conversion Perversion.
Sorry I can't help any more but it's about 2 years since I was thinking about doing this to my 356 speedster and the old memory is fading! Will look to see if I have any old files left on my other PC.
This thread:
http://www.shoptalkforums.com/viewtopic.php?t=119469
is a 13b in a VW Karmann Ghia and has just recently been finished.
This site might help as well:
http://www.geocities.com/zenjoe/vw.html
as well as this volks swap one:
http://frost.bbboy.net/vwengineconversions

Well at least if it goes wrong its only 1 of 3 parts

Here's a pic. of my rear engine Bremen Sebring.  I bought an entire 86 RX-7 non turbo and did a Camden supercharger on it instead...

Car was making roughly 305 h.p. at the crank at about 6 pounds of boost.  Mariah Motorsports had done the build on it.  If I remember right we were running a 600 cfm Holley Street Avenger carb on it.  Trans was a heavy duty build as even the rotaries can still tear up a VW tranny.

I thought of the 13B engine also. I wasnt sure how the transmission would work as i wasnt able to figure out what FWD trans would fit. I decided to look into the h22a honda vtech motor. Ittl be interesting to see the result of a 13b swap. keep updating//
see my question post for the h22a

Dave, I put a roary in a 914. It was carb'd and no turbo. You have to watch temp though. They are real touchy about that. They don't last long if you loose coolant for what ever reason. Like in less than a 1/2 mile. (experience) They are easy to rebuild too. You might think about using a 914 transaxle. Pretty much the same as a vols and have the solid shift linkage for a mid engine set up. Just a thought. Good luck on this. Lookin good.

   Ken