Being a 3 on the tree I suspect your truck is a F150, right?

I believe the 3spd should be a 3.03 3spd. And the input shaft should be 10T and 1 1/16" and most likely the 11" clutch.

 

 

I recently replaced the clutch in my '79 w/300 and a 4 spd. Re surfaced flywheel and bought a LUK clutch kit. Very impressed with it. Nice and smooth now.
Pretty sure the sixes all use an 11" clutch in trucks

 

I have two flywheels, a 77 and an 80. Both are drilled for 10" and 11" clutches. I read on another thread that the light duty trucks used the 10", while the heavier ones used the 11". On Rockauto, for a 91, for the f250's under 8500 gvw, they show a 10" clutch. For those over 8500 gvw, they show the 11" clutch.

I'm gearing up for a zf swap, and am using the clutch out of a f250 with a 351w. Bolts up perfect.

 

Under 8500 gvw used 10", over 8500 gvw had 11" clutches.

I'm surprised you liked the Luk clutch. I purchased one and it looked so rinky-dink that I sent it back to Summit. I went with a Ram.

 

RockAuto only list a 11" x 1 1/16" 10T for 77 F150's. But they also don't even list a manual transmission for the 77 F100. So you can't go by everything you see listed there.

I've had good luck with the Luk clutches for stock replacements. As long as you aren't going to be doing any high rpm clutch dumps they are fine. I bought a Valeo clutch for my 89 E350 manual swap.

The clutch company I avoid buying from is Zoom. I spent $400 on a clutch kit for my 54 project and it showed up with all the parts loose in the box and the zoom box destroyed. The zoom box was nicely packed in a damage free Summit racing box. I contacted Summit Racing and was told that is the way Zoom ships them. Even the dirt cheap imported clutches I've bought in the past have came with the parts vacuum sealed down or had some kind of inner box structure to hold it all securely down.

 

Well, maybe the Luk would have worked fine. My point is that 'it looked rinky dink.' By rinky dink I mean cheap, toyish, inferior, flimsy. So much so that I returned it. The difference in quality between it and the Ram was plain to see. However, I may have purchased a cheapo model of the Luk. Don't know.

Also, regarding the ten or eleven inch clutch: I had only looked at a 91 f250. There, I'm certain, you can see that Ford used the 10" on lighter vehicles.

 

I didn't see the clutch you got so I can't speak on that one. All I know is the ones I've bought looked fine. But it's possible they sell a economy version which could be crap.

Yes the 80+ had 10" & 11". I don't know on the 79 and older. But even if the 10" was offered why would anyone buy one?? The truck flywheels I've had, have all been drilled for both. So even if they came with a 10" I always buy the 11" for them.

 

No doubt, all 300 flywheels are zero balance so easy to use one from a later model vehicle if it's not drilled for 11".

I got a Ram 98620 clutch set when I swapped engines, it was pricey but the pedal action is easy and smooth. Noisy in neutral with the pedal out, though.

 

Both the flywheels I have are drilled for 10 and 11 inch discs. Are they not all so drilled?

 

ALL 1973/79's with a 300 I-6 have an 11" clutch. The only 3 speed installed in 1972/86 F100/250's is the Ford type 3.03 all syncromesh trans.