As further suggestion, move the "cheap test" to the front. Grep implies a foreach loop and is much more "expensive" than a simple equality test. The "if" statement is executed from left to right - don't bother with the grep if the first test fails.

Also consider the block form of grep:

if ($inext eq "Global.SAM" and
    grep{$_ == $F[1]} 73,89,121,101,117,69,77,67,115,81,97,65,113)
{}
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"and" is a lower priority operator than "&&" so no extra parens required.