I am putting a 2.5l suby in mine with a type1 swingaxel transmission with a flipped ring gear. (Outfrontmotorsports and Rancho)
The reason I went this way is that it is the simplest, most, done way.
You can go with the suby transmission, but then you have to figure out the suspension on your own. There is a guy on the spyderclub forum in Alberta that is going with his own dedion suspension and a modified 4wd trans with the plate from Australia to make it a 2wd unit. He has talked about all of the stuff he has had to make on his own, if you are a skilled fabricator and have the time, that might be the way to go.
The other way is to use the 914transmission (model915) , but the same thing is true for the suspension. My kit is set up for a swingaxel.
Thunder Ranch will take a 911 set up, and the Chamiox/Beck cars are doing an Audi/Golf/Polo car so that might be the way to go for the IRS setup.
Don't forget the plumbing for the radiator
Or just buy this one as it is already in Canada
http://www.spyderclub.com/phpbb2/viewtopic.php?t=12287