John, you will NOT be able to fit one of the big Dubro tanks into your H9 73" CAP without butchering the rear of the tank compartment and the second former. The tank compartment on this model is basically square. I had the same problem. The issue tank is typical Pacific Rim; IOW, not something I care to use.

The largest Dubro that will fit without former surgery is a 16 ouncer. That's not enough for the Saito 150 I'll be using, so I ended up fitting a four-ounce Hayes "Saddle tank", plumbed in conjunction with the 16 ounce Dubro.

I just didn't feel comfortable with removing any wood up there. This model has gone through several "beef-up" modifications to prevent the firewall from departing due to engine vibration and stress.

YMMV...

Steve