Basically, ANSI (US) keyboards have a horizontal enter, a full size left shift, and 104 keys. ISO (European) keyboards have a vertical "L" enter (an L but upside down), an extra key between the small left shift and the bottom-left alpha key, e.g. in the US, where you have |, there's just the rest of the shift key.
It gets more complicated if you want to swap the whole lot, as the width of shift, ctrl, alt and more vary by keyboard. This Acer (not ALPS, but takes ALPS keycaps) I'm using now doesn't even have matching meta keys -- right alt gr, win and menu have 24 mm spacing, but left ctrl, win, alt have 28 mm spacing. WTF? FILCO on the other hand make all the meta keys the same, narrower width as left shift.
Also, you may not have Windows and Menu keys depending on the age of the board.
Which keys are you looking to replace – if it's all of them, then a photo of the board would help so that we can see what size and shape keycaps it requires.