Sheet metal work isn't the problem. The problem is that you would be building what is mechanically a GS clone, and some of the parts you need for that are almost impossible to find. If you can locate all the right parts, everything fits without any cutting.
Naturally, you could put in a Chevy engine by using Chevelle parts, but for no extra work you could install a Buick 350 and keep your Buick all Buick. A Buick big block would be somewhat harder, but still nowhere near as bad as a nailhead.
Ray
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