BOP has it. Their part number is PPB126. They have the size listed as 1.3780 OD x .5906 ID x .3543

They say a 6202 is too wide. I don't know anything about 'em & have never bought one.

https://www.bopengineering.com/pontiac_replacement_parts3.shtml

A guy on Summit said this one fit his 455. Size looks real close to the BOP size. MAY be the same. Don't know.

https://www.summitracing.com/parts/ctf-43002/year/1968/make/pontiac/model/firebird

The Timken 7109 might work. But there are cheaper places to buy one.

https://www.summitracing.com/parts/tmk-7109/year/1968/make/pontiac/model/firebird

Rock Auto lists 3 different brands, with the part number 7109. National is the cheapest.

https://www.rockauto.com/en/catalog/pontiac,1968,gto,6.6l+400cid+v8,1256352,transmission-manual,clutch+pilot+bearing,1964

The National & Timken 7109 seems to be available most everywhere. They're just over $20 shipped, from several places.

https://www.amazon.com/National-7109-Clutch-Pilot-Bearing/dp/B003UE8DJI

https://shop.advanceautoparts.com/p/national-bearings-7109/3275450-P

https://www.ebay.com/p/74290259

https://www.amazon.com/Timken-7109-Pilot-Bearing/dp/B000BZ54UU

https://www.ebay.com/p/75888560

Shipping & tax will determine the best price.

https://www.carpartsdiscount.com/auto/clutch-pilot-bearing-bushing/pontiac~firebird.html?3593=1121070

Never have understood why the links I post work on every other site EXCEPT this one. Here, some work. Some don't.