Clutch problem I think

Thank you all for posting these questions and answers.
Everytime I work on my dart.
I research here... first.
My question today is for a stock 1964 273 4spd dart gt. What is the bolt size for early stock flywheels? I understand it will be going to 6 bolts from 3
I seem to read there are 2 sizes over the years
I'm doing the 10" clutch conversion.
On my stock 1964 flywheel. I want to pre order the required bolts.
Thank you for your time.