The 53 216 and the 54/early 55 235 engine had a high-mounted water pump with a 3/8" belt width. That's the pump you need to look for. Yes, the pulley is a press fit, and yes, it's TIGHT! Unless you've got a very well-equipped shop with specially-made pullers and a press, you'll be better off finding the correct pump. It's possible to machine the wide-pulley pump hub to accept a bolt-on pulley (I've done it) but then you need a lathe.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!