The amount of silver in predecimal coins is directly proportional: that means there's exactly twice as much silver in a sixpence as there is in a threepence, and so forth. That keeps the conversions between denominatons simple, allows you to "mix-n-match" denominations as you need to, and lets you work it out based on a "face value" in pence per ounce.
For sterling coins (pre 1947): about 71 pence per troy ounce. Three florins, or 6 shillings, or 12 zacs, or 24 treys, will all give you a shave over an ounce of silver. If you've got crowns, they're 60/71th of an ounce; a crown plus a shilling is a bit more than an ounce, or six crowns is roughly 5 ounces.
For .500 fine coins (1947-64): about 132 pence per troy ounce. Five and a half florins, 11 shillings, 22 zacs or 44 treys.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis