The "Marlin adaptor", for tang peep sights (actually a sub-base), is so the serial number (stamped into the top tang on most later models) isn't defaced ( a Federal crime) by drilling/tapping through it - not so the tangs don't have to be D/T'd at all for the forward screw.
BTW - Anyone beating on a ramped Marlin front sight blade, while trying to drive it in/out for replacement is in a perfect position to shear off the ramp attachment screws, unless the RAMP (and not just the barrel) is properly supported.
It's MUCH better to use a sight pusher tool - No fuss, no muss, quick. They're worth every penny, if you either plan on ever changing sights again someday, or shear off a ramp/screws w/o one.
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