1986 300D 5speed turbo

[88300D]

Hi everyone,
I have not been here for years as my 300D left me and took my wife with her.
I have just picked up an 86 with a 603.912 with an rb20 and a 5 speed from a 190e.

It has no tachometer if anyone can direct me.
It has the cruise stalk but no cruise, from reading in think there should be a controller under the dash. I have seen a plug on the inside fender that might be for it. Has anyone got experience with OEM cruise?
The box has a thrust bearing like sound with the clutch out.
I live in a hot climate and thinking of putting 30SAE in the box, what does everyone think?
(Yes I know the obvious of pulling it)

Thanks in advance
Howie