Technical Nailhead trans/gearbox adaptor identification needed

Hi Guys ,
I got this adapter plate with a bunch of nailheadand SBC parts I brought a few years ago,
The adapter is supposed to be for a 401'to adapt a GM gearbox or trans
I have minimal knowledge about nailheads ,and I'm trying to determine which years,this adapter may fit.
It looks like there are 3 different year ranges
53-56
57-63
64-66,
The adapter came with a crank adapter
Flywheel
Flexplate,
Centring bolts
Can anyone identify of give me info on what to look for in being able to determine what I have here as to what motor it may fit,
Thanks in advance