it's hard to tell from the pictures, the bottom mounting looks good enough to me, that welded fork thing should be more than strong enough to support that alternator so long as there are sufficient spacers in there to stop any sideways movement, it's important to bear in mind that those steel threaded inserts on the alternator mounting lugs can move as well, they do get effing tight but they are not captive and they can creep over time,

 

i dont like the top bracket with the slider, it's obvious why you've done it like that because you need to be able to adjust the tension, but the 6 rib poly v belts stretch over time and they need quite a lot of tension to keep them from slipping, i would prefer to see a spring loaded automatic tensioner on there..

 

the hardest part of that installation you have tackled really well by the looks of it, that is the horizonatal alignment of the belt, if they arent perfectly ligned up it will keep throwing the belt off

I really hope this makes sense as this is the best way to adjust tension, ask if you need clarification on anything. to increase tension, tighten bolt up

 

I don't really understand the schematic.
But I understand enough to get the principle..

I should set the tensioner up, so that I can increase/decreasion tesions, by turning a bolt.

you need to use the 3 mounting holes in the engine block at the lower bracket otherwise it will break the lug off the block with vibration etc. that alternator is quite heavy and will put a lot of strain on the mountings 

could you not just get the non power steering bracket from an older felicia of favorit?  the lower bracket is a cast housing that fits nicely to the block and supports the alternator. 

I could get a non power steering bracket from an older felicia.
But it would cost me alot, and it would be quite some effort.
Also, that bracket isn't compatible with the bosch generator, is it?

I have used 2 out of the 3 mounting holes in the engine block at the lower bracket.
You mean that I will break the engine block, if I only use 2 and not 3?