Ray, $400 sounds very reasonable to me to blast the frame and powder coat!
As far as us deserting you on advice, there's a fine line between asking general questions and asking for specific info. A lot of us hesitate to answer something of a specific nature unless we have either done it or know of someone who has. I have never put a chevy front end on a GMC, so I hesitate to say it can be done. I do know that the sheet metal is different enough that it would require quite a bit of fab work to make it work.
Be patient on your build and with our apparent lack of responses! Oft times, it give you time to think it through and gives you a warm, fuzzy feeling to have figured something out.
Thanks I appreciate it.