Hi From South Africa

[BigBob]

Firstly, a DR800 of that model is way too heavy to start with.
If you want to go down the route of rallying then start with a 750 from 88-89 as they are at least 20kg lighter to start with. A 1990 800 is identical to the 750.
Your model is completely different to the earlier models and most rally type bits will not fit.
The rear mounted tanks are impossible to find so you will have to fabricate your own like everyone else.
Stefan Hessler still rallies a Big and he`ll sell/supply just about everything you could possibly want http://www.dr-big-shop.de/

[nug]

You can shed lots of weight by getting rid of the twin exhausts & the steel underguard.
The frame is substantially thicker/heavier on the SR43 which is good for strength but not for weight saving. As mentioned, the tanks will need to be fabricated in which case you could make a complete aluminium monocoque rear tanks/seat/subframe unit to try to save weight.
I have seen people fit the Acerbis plastic tank from a DR650 but this means losing the beak & the character of the bike.
Stefan Hessler can do all the suspension upgrades for you.
For every Kilo you shave off, you will probably put back with the extra tanks etc.
It will cost a fortune unless you can do it all yourself.

I fitted a Wilbers rear shock & Drz 400 front forks to my SR41. It made a world of difference to the off road handling but very little improvement to the road handling.

Good luck with the project & post some pictures of any work you do

[nug]

Sounds like you have a plan

keep us informed.