Hi Ralf and Welcome to the Forum.
If you want to get back to the 1969 specification, I advise you to be careful. Most of what you see in the brochures is for later, 1970-on, bikes.
These 1970+ bikes are often referred to as the First Series (“Prima Serie”) of the wide-case Scrambler. In fact, this is incorrect because there were two (!) earlier models, both of which appeared in 1968.
Your problem is that 1969 was a transition year between these early bikes and the ‘Prima Serie’ bikes.And I have to tell you that, to my eyes, your bike has many characteristics of a Prima Serie. You have a VHB carb, not a SSI. You also have the large air filter. The instrument mounts are Prima Serie, as are the black painted headlamp brackets and the paintwork on the tank. The mudguards are painted the same colour as the tank, as for Prima Serie. You have the short silencer … and so on.
Also be aware that US market bikes and European market bikes were slightly different.
Btw, your rear light mount is not what is normally seen on a Scrambler. It is normally seen on the RT, 1970+.
What I’m saying is that if you want to get back to a ‘1969’ specification, you are likely to have a lot of cosmetic changes to make. Nonetheless, I will try to reply as best I can to your questions
Ciao
Craig
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a) Which original colours were available in 1969 on an 350? Only orange? Orange together with a black stripe or without it?Red seems to have also been an option, at least on the 250. From what I can discover, some bikes had the black pin-striping, some not.
b) Which air filter is the right one? The big ugly black one or the smaller one connected direct to the carburettor?The Big One is correct for a VHB carb.
c) Has the fuel tank silver-painted panels or was it chrome plated? Was the shape like a drop or does it had a recess in direction to the seat?Your bike appears to have the chrome plated panels of a Prima Serie. The tear drop shape is correct for a Prima Serie.
d) How were the instruments mounted? In two separate brackets or one for both? Prima Serie, two mounts. Before that, there was only a speedo in the headlight, no rev counter.
e) In original condition the shocks had rubber guides. Correct?Yes. And same for the front forks - and that even for the 1968, pre-Prima Series models!