Question: can I take a Stanly jack plane and round the
blade and get the same performance?

Doubt it. Scrubs tend to have narrower blades. Plus the throat opening must be
much larger to allow the large chips and chunks thorugh. The chipbreaker is
another factor to consider. By the time you are done, you wil leither hve a
scrub that does nto work, or a ruined jack plane.

Get your self a simple Knight scrub, or an ECE one. I prefer wood planes,
especially in scrubs because you are moving it a lot, and the lightness of a
woodie helps. It has less mass, but you are not taking long steady strokes
where chatter kills you.