I have a 1965 Paramount track bike with serial # W74, and it was built in
first half of 1965.
I have owned from that time. Go with the 1961 date. I have a Schwinn
factory serial number prefix list which would make H75 appear to be a 75 model, but
in 1975 seial numbers started with a letter followed by 4 digits. The letter
was the month, the next two digits, the year and the last two digits, the
frame number for the month.
H7534 would be August 1975, the 34th frame produced during August.
Dave Staub
Orange, Ca