Using a larger size disconnect is fine and will have no affect on anything.

You will find that a 60amp disconnect uses the large fuses that are only available in 40amp and above, although you can use the smaller fuses with a reducer.
30 amp disconnects are not uncommon and should be available any big box store.

There is no reason to put any fuses in, but if that is the only disconnect readily available you can put any size fuse you want that is 30 amps or larger.

A couple of 60 amp fuses would be acceptable, as would a non-fused disconnect.

The CB is providing the over-current protection already.

Thank you all for the replies.
I wound up getting a GE 60A non-fused disconnect.
The guy at the store said they no longer sell both 30 and 60 amp NON fuse disconnects because the box is really serving as nothing more than an on-off switch and that it is the circuit breaker in the panel which must be correctly sized....so BRICKEYEE you are right on the money. Thanks.

There was a real lag by some of the condenser manufacturers in having their equipment listed for use with circuit breakers.

Thuisw meant that fuses were required to protect them (even when a circuit breaker was installed in the panel feeding them) and the disconnect was a simple place to put the fuses.

I have not seen any new equipment in the past 5-10 years that was not circuit breaker rated (And most residential breakers are also HACR allowing their use) so the requirement for a fuses has gone away.

Volume production lowers cost, and the price difference between a 30 amp and 60 amp is not enough to really justify the smaller device.