Here's the deal.
If you look in the 1969 AIM (UPC Z28, sheet A4), the motor mount (item #4) states that it's a "PRODUCTION PART". This means it's the same as the base V8 shown on UPC 6, sheet B4, item #2, P/N 3964895, which is a non-locking mount).
The September, 1968 P&A 34 shows TWO service part numbers for the 1969 302! The first is 3886466, which I believe to be the non-locking mount, and the second is 3939728, which I believe to be the locking mount (see attached). No dates given for any changeover, so that's of no use at all. Another kicker is the September, 1968 P&A X691A shows P/N 3939728 as being used on the 302, the 350 AND the 327!
The 3990918 part number doesn't show up until the 1970 P&A, so to be "factory correct", you have to have the 3964895 mounts.
The problem is, it's not longer available. It was superceeded in January of 1971 by P/N 3989488, which was then superceeded in January of 1973 by P/N 3990914.
3990914 is shown in the 1972 P&A as being used in the 69 Camaro with 307 or 327, and P/N 3990918 as being used on the 69 Camaro with the 350, 396 and 302 engines, so somewhere along the line, things got really cobbled up.