727 transmission servicing question

I am about to drop the pan on a mid 70's 727 transmission to change the filter. It has the stock pan. Can someone give me a approximation of how many quarts of trans fluid I should buy? Thanks

My fuzzy memory says 6. Don't dump them all in at once though,don't want to overfill.Put in 4 ,start up and check fluid level, add as needed.

I'll agree with the 6 qts to buy
But there are several variables involved with this question.
I'd start with 2 or 3, Cycle through all the gear positions and add as needed. If cold, leave it 1/2 quart or 1 pint low until at operating temp as ATF expands when warm