Welding Cab replacement section.

[satexasuser]

I'm rebuilding a 01 f-150 super crew and will be replacing part of the driver side cab with a salvage replacement part . I'm going to cut out the damaged piece on my vehicle and weld in the replacement pieces using a MIG Welder. My question is when I join the metal pieces toether (new piece of cab with existing cab) should I weld only on the inside of the cab or on the outer cab also. Also once the welds are in place how fine can I grind down the weld an it still be safe? Sorry for all the questions but I'm going to give it a go. Here is a pick of the cab part I'm going to replace the damaged cab with (http://community.webshots.com/photo/348475344/365711283VfsVba) . and here is my damage truck which I will cut out to replace (http://community.webshots.com/photo/348475344/364938764JOYvxe)
Any pictures or advice would help
Thanks

Mario
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