replacing rear arch

[iluvmud]

Okay now its looking like ill have to replace the whole arch so How hard is it to do i am pretty useless at all things mechanical  and wondered how much work is involved and how easy it is to do ?? Is welding required to put the new arch in in the haynes manual it doesnt mention welding just pop riviting but the arch as pictured below seems to be welded to the body where the door seals are ??  

Any advice or tips greatly recieved people !!

[Dave Rogers]

hopefully the C post is in good condition, check with a screwdriver in a stabbing motion, if it goes thru, the post will need repair. Bear in mind that the arch is part of the C post and an mot fail if any part is not substantially free from rust.