Not sure on the pump, and asked a similar question on the rams a while ago. My rams had a "6K" or "K6" stamped in the base, which I assumed was a Oct 66 date code.
http://www.concoursmustang.com/forum/index.php?topic=7875.0On the pump based on the fill nut on the end looks to be a mid 70's to late 80's model. The originals (used 65 thru the early 70's) had a fill plug on the side, can't tell from the photo but does not appear to be one there, only on the end. Most were not Mustang specific and used in a lot of different lines.
Some info and photos that may help here...
http://www.topmotorrepair.com/On the rams I think that they are also "later" ones as I have seen mention of early ones with nylon/plastic bushings embedded in the pivots, yours do not appear to have these which would align with the (apparently) later pump.
Appears to be a mystery area, as details of convertible parts are not generally noticed in judging standards.
HTH