Hi.
I'm planning to put a 1400hp T58 turbine with arneson or speedmaster drive on a 50' scarab, the boat will wheight less than with triple BB and much less than with two big diesels, but will it work? Would the boat be controlable? Would it get up on plane if i use a 6blade prop?
It is the best choise for less money than other choises.

Seems like that is a biiiig boat to try to get on plane with one wheel. Initial thought is they built those boats with triples for a reason and I would be surprised if you can get the thrust you would need with a single.

Single turbine with a splitter box into two drives perhaps?

the answer is simple.. 2 turbines!!!!

But still it will lose pretty much wheight in the stern with just one turbine and drive, the boats wheight is 6800kg with triple 420 and trs drives, with big diesels it would wheight ~7200kg and with one turbine ~5900kg.
Don't you think that with this much wheight gone it would be enough with just one?

You might even worsen the ride with taking weight of the back.

I'd go with twin diesels and surface drives. That's how the factory did them too.

The factory made them with 3 420hp V8's and trs drives

They were also rigged with twin Cats and ASD8's

Ok, i did not know that.. How many hp's and what model?

The Cat engines in that era were 3208
V8, 636 cu in, and rated as high as 425 HP in marine dress

As you'd know by now Yachtmaster on the forum has one (the only one?) mentioned by Rick and equipped like Huge tells originally in Helsinki