I have three frames in question. The first is a Ventura 24" 10 speed I picked up used in Alameda in the early 80's for my girlfriend. It had a thick layer of dust so maybe it's a 76 or 77?
W76 9 60130
The other two were hanging in a bike shop for years. The shop went under and they sent them to the junk shop here in Olongapo, Philippines. I bought all 7 frames I found there, these two were the only ones that weren't locally made.
The 27" Mixte serial number is IK87012072
The chrome frame made for wide 26" tires is A87111415.
There are no other markings on the frames. I don't see how to post pics.