How hard is it? I'm not the best welder in the world, but I was just wondering how hard it is, and/or what would be a reasonable price to have it done (mechanical stuff is fine, but body work... I'm out to lunch).

I would like to do a body lift, but I noticed some issues under the front mounting blocks (mostly drivers side, but I usually do things in pairs).

Here is the part in question:
http://www.lmctruck.com/icatalog/cst/full.aspx?Page=47

Item #1.

Thanks in advance for any help.

Should not be too difficult. You will just want to brace the body properly after removing the mount itself, then the mount box. Drill holes around the perimeter of the new mount box for your plug welds in.