Though I don't have any experience crossplaying it sounds like you'd just want to wear a binder first then put an appropriately size bodysuit over that, muscles or no. Then regardless of whether or not you get the muscles you'll at least look flatter like you'd want.
You'd probably get more response for how to build the muscle suit in the sewing forum, it gets brought up there occasionally so there may already be threads to search for it, too. Also I've seen some Jojo musclesuits that looked amazing, somehow realistic while also looking cartoony (which I understand you may not want this being SH) but they could also be a good reference.
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