Well I finally got around to getting the diagram edited, and uploaded.
Back in the early spring, Chad ("71airstrike" on the Corvetteforum) put in a C4 fan motor to get more air flow out of the vents for the AC and heater. It worked great!

We did make a rough diagram of the spacer that you will need to make for the larger squirrel cage to fit the C3 fan box, just print it out as a full size 8 1/2 x 11 page, and the dimensions should be correct.

Probably the best material to use would be some marine grade plywood, the thickness was about 1/4 inch.

Drill out the "pin" locater holes with 1/4 inch bit, and the bolt holes to fit.
We also used a dremel with a sanding drum to radius out the insides to fit the squirrel cage on the new fan.

There are only 2 wires to the fan, polarity is easy to check, hook it up to your battery to make sure rotation is correct.

Also, it really helps to seal all the exterior ducting from underneath the car after the new fan is in, you can really tell where the leaks are with the amount of air the new fan pushes...

NAPA Part number: BK 6551778
Price: $ 58.99

Link to full size drawing:
http://temp.corvetteforum.net/c3/desert ... spacer.jpg

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Arizona Corvette Enthusiasts
Gone, but not forgotten

Great idea!!! Thanks for posting the details and sharing the idea guys.This is going directly into my "to do" file.
Thanks again
Jules

Forgot to log in.
Jules

I did get one after picture of Chad's installed spacer. I hope it helps.