Someone posted this 1971 spec page.

I noticed the four had tubeless tires but the six had tubed tires.

Can someone please share why they were different..

I'm going to guess it's the speed rating available with the skinny tire/wheel combo?
Weights seem low.

IIRC the 5-lug steel wheel was a carry over from the 911/912 in the non-tubeless type steel wheels - so a tube was required; but I also think that the -6's optional Mahle & Fuchs 5-lug alloys were tube type wheel.

So they actually came in both tube & tubeless flavors.


Tom
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If I recall, when I got my -6 with steelies and 185/70-15 tires many years ago, they all had tubes. Kept them that way until I had to have a tire removed/reinstalled for some reason and the kid at the tire shop had no idea what to do with a tube tire (apparently). Got about 5 miles away and a rear tire blew out at about 50. Shredded the sidewall so had to get new tires (the shop of course said it wasn't their fault..).
Put in new stems and been running as tubeless the last 30+ years without a problem.

Early 911 wheels like the deep 6" Fuchs didn't have the tubeless "hump" formed on the inside of the rim. Supposedly this keeps the tire bead from slipping to the inside of the rim and sudden loss of pressure. This could happen with low pressures and severe cornering. So they used tubes like most early cars.

go hear for all you want on the patent

https://patents.google.com/patent/US4606390A/en

Click to view attachment

All rims without an inner bead should have tubes. Yes you can get away without tubes but you're definitely taking a gamble.