Direct fit is always preferred, going to try the Allmakes ERR3443 aftermarket replacement, which is supposed to be a standard duty drop in and pretty close to the cost of the Chevy. Will let you know how it works out

 

Sooo the replacement fan clutch arrived, supposedly an Allmakes (which I've had pretty good luck with in the past) ERR3443 tho there is no marking on the part or box so there's really no way to tell who made it, the old one came off easily enough via the usual methods and the new one fit perfectly, and there is a noticeable lack of vibration so I guess my old one was wobbling more than I gave it credit for. However.... holy crap does it howl. Starts with a deafening roar and sounds like a jet plane taking off, even stone cold on a 30 degree afternoon. I made sure to order the standard duty, but maybe that's not what I got ? No way to tell with no markings on the part. Do these things need to break in ? Man it's loud, and no noticeable reduction in temp to even make it worth the annoyance. So far I'm pretty much underwhelmed, I'm going to drive it for a couple days and if there's no noticeable improvement, back it goes and it's off to the box store for the chevy part and some instant gratification.

 

I've never used an Allmakes, but keep in mind yours probably wasn't working really well and not engaging fully, so this one will be keeping the fan engaged more.
Also, viscous fan clutches need to be store upright otherwise the fluid migrates to areas it's not normally supposed to be, so yeah, an break in time is probably needed. At most a day though I expect.
Even the Imperial standard duty is louder than a worn out clutch.

 

If you've never used an Allmakes fan clutch, don't. After two days, 400 miles, and countless gallons of gas, back it goes. The howl was annoying during local driving and deafening and ridiculous on the highway, if anything it seemed to get worse with time and distance but it was probably just me getting more and more fed up with it. And the effect on gas mileage was impressive, a trip that normally takes 1/4 tank took 3/4 today. Temperature seemed to make no difference, hot, warm or cold it just plain sucked. Maybe it's a bad one? Don't know, don't care, it needs to go away now. I replaced it tonight with the Torqflo standard duty Chevy part from Autozone and some 10mm cap head bolts from the hardware store, and not only is the howl and roar gone, but it's back to running a couple degrees cooler like it used to.

For those having a similar fan clutch issue, some lessons learned....

1. Listen to the majority of people who have done this before, the Chevy part works, the fit is great.
2. The bolt holes in the fan only need to be opened up a few thousandths to clear the 10mm threads, I used a 27/64 bit because I had one and the standard 3/8 bit doesn't quite give enough clearance. They center perfectly on the Chevy clutch, just need a little more diameter. You can still go back to the OE part, because the fan centers up on the centering ring on the clutch.
3. Cap head bolts will ensure no interference with any of the features on the surface of the clutch. A little loctite on the bolts holding the fan to the clutch will ensure they remain where you put them.
4. 36mm wrench, long enough to extend over the top of the radiator frame.
5. Position a crowbar between the water pump pulley and the belt tensioner for leverage and just get a little pressure on the pulley, just enough to stop it from turning. It doesn't take much, and too much force will cause another opportunity to work on your truck and replace things.
6. A sharp rap on the wrench with a hammer (I used a 2lb mallet and didn't have to whack very hard) breaks it free

Why the Autozone Torqflo part and not Advance Auto or Napa or anyone else who carries the Imperial / Hayden Chevy clutch ?? Well, I'd like to say it was because Abran had such good luck with it, but that's only partially the reason.... like fingernails screeching down a chalkboard I just couldn't stand it any more and simply passed by an Autozone first, and cut off two lanes of traffic to get to it.

 

I forgot to mention I am the main stockholder in torqflo products... Thank you for buying!