I've done this more than several times, made "reproduction" Therm A/C cleaners for this application (L48 auto w/mandated ZL2 air cleaners like Pace Cars). You'll need a donor 2 or 4 bbl period air cleaner (use a 2 bbl if you don't want to sacrifice a 4 bbl), hopefully complete with the green 4bbl vacuum valve and the hose clips on the bottom of the air cleaner - you'll need these to make it cosmetically correct amd functional, too. I carefully remove the snorkel without damaging the flange, drill out the spot welds holding the clip, then spot weld the snorkel to the cleaner body after spot welding the clip in place (only way to spot weld the clip is to reach through the empty snorkel opening with the tongs and spot it twice to position it and keep it in place). Do it this way and, as William says, it's undetectable.
No, the base is not date coded (I have an NOS ZL2 cleaner in the box to base this on). Remember, early ZL2 cleaners had a flat bottom where the filter sits, a raised rib version was a second design and the first design to be reproduced. Flat bottom cans are in reproduction if you want to use one -
ZL2 manual or automatic air cleaners all used painted lids, not chrome -
Regards,
Steve