225 Slant needs a good idle. what rpms are you spinning?

Well
Dan
is right
For proper low-speed operation the Transfer-port sync is very important. And this sync operates quite far up the rpm band in neutral. I'll wager you can hit 2500 on the sync, and maybe 3000, even.
The factory made it easy for us to hit the sync point by specifying valve lash,the idle-rpm,the idle-timing, the rate of advance, and the power-timing is built-in. If the engine is fresh, or in good working condition, and factory stock,then you will not improve on their specs. Sure you can dick the timing around or dick the sync around, but in the long run, and for hitting the most targets,you won't make it any better.
But if you like 580 in gear, and like others have said,if it doesn't hesitate on throttle tip-in, and the oil-pressure is ok,then enjoy it for what it is.
Now, if you modify that engine, then you get to re-engineer all the tuning requirements, to hit as many targets as you can,starting with the T-port sync. When you are done you can print up a new spec sheet, for following owners.

Having said that, I remember this one engine I had, that made this wonderful thoop,thoop,thoop,thoop,thoop sound at a way-too-low idle rpm. That was a 69 340 with a complete 318 top end on it including the cam, but with fenderwell headers, in a 65 V100 wagon, with 2" straight pipes out the back, and little Thrush shorties.
Thoop,thoop,thoop,thoop,thoop,thoop,thoop,thoop,thoop,thoop,thoop,thoop.
I bet it was like 500rpm in gear,lol.Maybe less