I use one in my car, no problems so far. I've changed most of my ratios with Albins gears.

There are two types of rear extension housings, have got pics in my photos.

Some info on them for you.

http://www.dellowauto.com.au/main.html Download the catalouge and it gives you some info on the type of box and what ratios are in it.

http://www.billzilla.org/

Hope this helps.