Yep, August 1969 on this one. The movements are extremely similar. All 45XX are I guess. It all started with the Lord Marvel 36000 which was the proof of concept 36000 bph movement.
The only other vintage 36000 bph are all autos and don't have a no date version - 6145/6146, the more accurate 6155/6156 and the ultimate VFA 6185/6186 - super expensive.
Btw there are 6146 watches in HSS - hardened steel. Also I think there are some exotic 6185/6186 cases.
There are also ladies movements which are 36000 bph btw - 1944 and 1964. I think they are very nice for ladies.
Anyway as far as all of these go - my grails are 6186 and the elusive 4580.
I don't have any 61 though. Just a bunch of 45XX. Sadly no 4580 either.
Btw your 4502 is nice, minty condition just like I like it.