Marantz 250M pre-driver equivalent?

Hello;

I am currently working on a vintage marantz 250M pwr amp. I found there seem to be some strange transistors inside... I searched on the web aswell as in this forum, but wasn`t able to find some information.
Currently I am searching for a pre-driver in a TO-39 metal can housing; the name of this item is S39613.
Anyone happened to work on such an amp - which replacement is suitable? Why didn`t those guys use regular transistors:bawling:

thanks, audiomatic