Just out of curiosity do you have to use a transmission with speedmaster drives?

yes

To second that

YES

I have #3 drives behind 750 Cobras w/ transmissions

You can also use crash boxes

You only "have" to use transmissions if you want your boat to back up or sit still if the motors are running.

I'm not trying to be a smart@ss, a Donzi nut (goes by Geoo) has a zillion horsepower smallblock 18 footer with a DIRECTDRIVE Arneson (to save weight and space).

My old outboard dragboats had no teeth on the reverse gears to save on friction and were locked in forward.

Some of the turbine boats use direct drive with a "brake" on the output shaft to be able to stop the prop around docks without spooling down the motor.

Speedmasters and TRS drives have no shifting capabilities inside them.

So are there any drives other than TRS and SM that do not have shifting capabilities? How about Arneson, Pulse, and Kamma?

Arneson, Pulse, and Kamma?
They all need trannys too.
And they dont reverse rotation in the drive. So you need a tranny that has full power capabilities in both directions, or you have to reverse rotate an engine.
Probably more than you wanted to know.
Gary