A few are still incomplete from the 50s:
Thanks in part to Pete Palmer, I have added composite box scores for all NBA Finals dating back to 1950. There are some holes in the data: minutes played are missing for the 1952-1954 and 1956 Finals; field goal attempts are missing for the 1950 Finals; rebounds are missing for the 1953 and 1954 Finals; and assists are missing for the 1950, 1953, 1954, and 1957-1959 Finals. If you can help us fill in any of these missing values we would love to hear from you.
but they've done a great job putting this data together. The remaining stats are going to be hard to come by since it seems no papers at the time published 'complete' box scores, and articles only mention high rebounders/playmakers. They're not far off from completing the project though, so it's pretty neat (hopefully they add Finals stats to individual player pages).