well I did it :-) well chuffed. Thanks for help guys. It wasn't as difficult as i thought. Garage quoted me 450 for the part+100 labor to replace the alternator. I ordered this one for 99 delivered from ebay. No garage was willing to put customer provided parts. so I decided to do it myself. and after succesfully replacing the alternator i am getting 14.6 v (with buttonmod) from it to the battery. problem solved :-)
I will list steps here for anyone else in my situation.
Prerequisite - Good socket set . (cheap ones will be destroyed as bolts holding the alternator are quite solid. after breaking 2 cheap ones i had ,i bought this one from halfords . - Camera to record steps so that if you forget anything you can see it back ( I might upload my version) - a long wrench to hold the tensioner in place
Steps Remove the negative battery terminal remove the black big air chamber by removing a bolt and two jubilee clips holding the hose connection. once the air chamber is out. you can see 2 bottom nuts which needs removing but hold on. now see the location on tensioner in your diagram for your car next to your radiators. put the long wrench on the tensioner and push it back towards the dash. then belt will loosen and you can take the belt off alternator. now you can secure the wrench in same place by resting it on another wrench or bat in horizontal position by creating T like structure. (this saved me hassle of re doing the whole belt.) Remove the 13 mm bolt connecting battery to alternator Remove the Clip connection once belt if off unbolt the top plate by removing 3 bolts. once the top plate is off remove bottom 2 long bolts. now use a pry bar or hammer with pry ending to wiggle alternator out. Follow the reverse process to fit the new one.
