71 350 stock fixed fan, no a/c, 4 spd. I would like to switch to a clutch fan. Any reason not too?

 

"A thermostatically controlled fan clutch is used on all cars with air conditioning, heavy duty cooling, or W-30 option", 1971 service manual. No difference if manual or automatic I could see, maybe it would cool too much? it works thermostatically so that should be cool. I would go for it myself, I like mods that are easy to put back, It's not like a cam change or anything. Make sure the spacer is the right size, it makes a big difference in cooling where the fan sits in relation to the shroud.
The size and number of blades usage chart for different engines and body types is in the manual too.

Allan

 

If you're going to do the clutch fan (which I would just on principle) you might want to look at putting in a HD water pump, and fan shroud to direct the cooling. The HD water pump will give you the proper spacing that you will need for your belt, but you will need a new pulley to fit it because it bolts in "backwards" compared to the original cooling fan you probably have. And if you're doing that, may as well put in the rubber gaskets around the rad, and bottom air dam behind the bumper that funnel the air for HD cooling.

You can probably get all the parts you need used for under 200 bucks. Been my experience that the fan shroud is usually the most expensive part. Fans, fan clutch, water pump I got some new some used for around 25 bucks each. My shroud is new and cost 90.00. The gaskets cost around 45.00 new for everything.

I'm doing this to my car, and there's absolutely no downside except it costs money for the other parts. Like Allan H says though, it's easy to put back to original if you want.

 

Thanks for the good info. I do have the factory shroud and gaskets. Time to start collecting parts.

 

Uh, backwards? If by this you mean the fan clutch uses studs in the water pump flange instead of bolts, yes. I'm not sure I'd call this backwards, however. You don't need to change the water pump. A fan clutch on the non-A/C pump will work fine. As noted, a HD pump will require a different pulley to match up due to the different pump length.