Replacement for Aqua Magic

[Julison70]

Hi, I have an Aqua Magic Model 70 in my 1969 Caravel.
The main Valve leaks and I Need to replace it. I read some forums and based on that I ordered the Dometic 310. However the final height is 27.5 inches due to the platform in the bathroom. I will try and exchange for the low profile 301 which is 10” shorter. However, the flange provided with the 310 has no threads and cannot screw into the black water tank. What can be done to join the new toilet securely to the black water tank? Are there nee threaded flanges that can be purchased to fit the old tanks?

Thanks in advance,