This tripod extends to 8 feet which is great for getting some shots.

But it does not have a leveling head.

Does anyone make a leveling head for this tripod?

You can use this one spirit level on top of your camera.
: Kaiser Hot Shoe Duplex Bubble Level 206387 B&H Photo Video

Frankly speaking, leveling a stills tripod is a pain as you need to work on individual legs to balance.

Gitzo themselves make a leveling base - this one: Gitzo GS5121LV Leveling Base GS5121LVL B&H Photo Video

I have one fitted to the 1348 and it works just fine.

I'm asuming the 1548 has the removable top plate that allows the fitting of the bowl/base?

Yes that's the current leveling base from Gitzo and yes it fits the GT1548. I use this combination and it's great.