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ya i want to keep my stock bedsides intact
It is a slow process to get them to look right and I honestly don't think its possible to save your old bedsides without damage and remount them. Too much needs to be cut from the bed itself.
Alon is right there is an easy way and a hard way. Also slapping them on there is easy, having them look correct takes some time and patience. At first I said no way I am cutting and spent two afternoons drilling all the spotwelds on one side. There is a row along the inside edge of the bedrail and if you remove them the top will be weak when you mount the fiberglass. Hannerman recommends cutting because it leaves more metal and strength. I gave up on drilling and cut the other side off in a few minutes with a cheap jig saw and metal blade. In my opinion it is no doubt the way to go.
You will need a grinder to remove the metal under the taillights or it will hang below the fiberglass.
Take your time when mounting the new panels to be sure they are straight. If you don't cut enough they will be higher than the old bedsides and not be straight with the cab. Also pay special attention to the clearance between the cab and bed. It took me a long time to get that line parallel.
You will need to make mounts along the inner fenderwell or you will not get the correct bulge and they will flap around. A simple bar running from the bed to the fender lip works. I can take some pictures if you need them.
Here is a link from when I put mine on. There is a few pictures of the cutting at the bottom of the post.
It will be worth it when its done.