Chevelle Fiberglass

I have a 1970 Chevelle and was planning on painting it in the spring. I need to make up my mind on replacing some parts with fiberglass or keeping the sheet metal before I paint though. So I was wondering if going fiberglass is worth it.
I weighed out how much the fiberglass hood, trunk, front fenders, inner fenders, and doors would weigh which is about 70lbs. I couldn't find fiberglass quarter panels or roof-- could this be because there is no way to attach them? I was trying to find the weights of the sheet metal to see how much weight I would lose by doing this, but can't seem to find them.

Does anyone know the weights or where to find them?

Aside from painting, is there anything else I have to take into consideration when doing this? I couldn't think of anything but I could have overlooked something.

Thanks in advance for your help