Sanden makes hundreds of compressors, all with slight variations such as:
- Port location (horizontal or vertical)
- Port thread size
- wiring connector type
- Pulley size
- Dimensions (a,b,c,d,e) shown on their website.
http://www.sanden.com/index.php?productsearch Vintage Air supplies a 6668 model with their kit.
4664, 8104, 4639, 4644 & 4647 are all direct replacements for the 6668.
I used a Vintage Air bracket and a #4471 so the fitting would come straight out the back (horizontal) versus the vertical ports on the 6668 for my 340 install.