Need Help

[Only1Glendale]

Me and my dad are going to do a project car to create a reliable vehicle for me. We both agreed to go older so we don't have electronics to mess with, just pure automotive mechanics. After looking at several makes and models over and over I have fallen in love with the older GM trucks. However, I am having a real hard time finding the information I need to figure out exactly what I want to do. So if anyone can help me with a link to somewhere I can find this info or if they can recite it on hear that would be amazing. Even with all my googling ability google hasn't answered any of these questions. And yes I have looked at a lot of the threads on here but they all show pictures and don't tell much on results.

#1 Can the GMC 2 headlight housing and grill fit on a Chevy?

#2 Are the beds completely interchangeable? Like can I put a c10 stepside on a K2500?

#3 How much horsepower can you get out of the different engines? I want to know this because if a straight six can get me some pretty good power i might be more willing to let go of the 350 idea.

#4 is there any way to find out exactly how much horsepower different add ons will give you? like Stroker kits, different carbs, and what not?

#5 MPG? There was no EPA back in the day (thank goodness) but I do care a little bit about the performance fuel wise. Ideally I would like to figure out a good engine tranny combo that will get me decent mpg when I am light footed and pull some power when I floor it. There's no real info on what a 350 or 383 or straight six get on the c 10 and k25. Nor is there any clear data on how much MPG I would lose going with K25 over a c10. My dad estimates 9-12 mpg with the K25 since its 4wd (if I understand it correctly) but I personally find it hard to believe its that bad since a 350 can get more horsepower than most engines these days and the weight of these trucks are similar to cars these days since stupid safety standards have added almost a 1000 pounds of extra crap onto vehicles.

If even one of these questions can be answered it would go a great deal in helping me figure out what exactly I wanna do for a project. I love all the great projects you guys do and some of them are completely amazing. However, since my dad hasn't welded in forever and I would probably blow up the block trying to learn how to use one he refuses to do any major body changes. I do wanna say I love every ones creativity and acceptance. One reason I chose a truck instead of a car was because the old car communities are complete purists and hate customization.