Heavier bridge, less break angle over the bridge (adjust tailpiece so it is higher above the head).

Smakula Fretted Instruments sells skin heads.

I'd say first just lower the head tension and see where that gets you. I like my bluegrass banjos up at like 91, but seem to like my ITMs down at like 85-86ish on the drum dial. This make a much larger difference than the head type, in my opinion.

Head type does makes a difference, but I can't say myself I'd want to mess with a real skin head changing tension based on the weather. Remo makes a fiberskin type head that's supposed to sound similar to skin, but is mylar and doesn't have weather issues. Those get REALLY dark, maybe further than you want to go.

It looks like a goodtime artisan comes with a top frosted head. A renaissance (sort of cloudy translucent) or white suede or black suede head will knock the edge off the brightness. It seems the renaissance is the standard for ITM, but I'm beginning to like the suede heads as well.

Looks like a goodtime artisan comes with a presto type tailpiece. If it's adjustable, set it so it's further away from the surface of the head, almost to a straight line from the bridge to the edge of the banjo. This makes a large difference as well, and won't require swapping parts.

If you want to play with a real skin head, Smakula Fretted Instruments sells them (and usually has good prices on regular heads as well).

I like Renaissance heads for this very reason. Takes just enough brightness out of it. I also use Scorpion bridges with a wider top

John Balch for hide heads hidebanjoheads.com/shop
I like 'suede' style plastic heads (available from smakula fretted instruments), but hide can sound amazing.

Thanks everyone. It does have a renaissance head, so I will take some of the suggestions here, to see how it goes.
I had no idea how much fun the 4 string Irish can be. I play guitar with a Celtic group, and one of the guys had one. I’d quit playing Scruggs a while back, but having a banjo in my hands again is a huge joy!