I‘m gonna guess 64 based on the radius of the circular part of the numeral. The unclear one in question seems to have a smaller radius than the 5 and closer to the 6.
I’ve seen lots of sloppy stamping on the bottoms of various Wilton bullets.
The numeral 1 is quite profound and the second 6 is faint on both examples. Thanks for sharing. Would the hammered green be the correct color for in 1959?