I wanted to do a fan upgrade with as few changes to my rig as possible. The original metal vents look cool, and will probably last another 47 years, so why mess with a good thing? Inspired by another post, I decided to have a go. My results are a bit different, so I thought I would share.
I found a 10" 12V
radiator fan at Advance. While I might have found something cheaper online, I liked the option of seeing it in person and talking to the friendly man who works there. Here's a link: Imperial Electric Fan - 10" Diameter 226110: Advance Auto Parts
If you read the directions (which I am loathe to do), you will find that the BLACK wire is positive. This is important, since the blades operate MUCH more efficiently in one direction than the other. If you wish to reverse the direction, don't worry. Just flip the blades over AND reverse polarity. If you plan to use the fan in both directions when installed, you should probably find a different (straight?) blade configuration.
Although rated for 5A in the specs, a quick check showed actual draw at 2.5 - 3A, depending on how much resistance is provided to the airflow. The blades interact with the shroud to produce a secondary sound, sort of like a turbine. So, I elected to install without the shroud. There is still a bit of a whine at full power, but the 120VAC fan I use on shore power isn't exactly quiet either, and the outputs seem similar.
Now on to the fun part. The whole installation can be done with a 3"x5" piece of 7/8" thick wood, with a slot routed out of it.
The second photo shows what the slot is for. One of the bearings and the wires protrude out of the back side of the motor. This makes a passage for them.
The third photo shows the install. The fan itself is attached to the wood with two screws. The wood is attached to the original fan struts with two screws.
Note that there is sufficient clearance for the fan when the cover is closed. Little people like to flip switches. This avoids burning up a motor when that happens. A little sealant protects the wood from moisture, and that's it. I will probably install a shroud at the top to increase efficiency. I also plan to look into the PWM power supply featured in another post. But, these have been well-covered by others.