[dsraven]

i'm on the "get the fuel out of the cab" side of the fence. I have been around lots of these and other old trucks with the tank in the cab. they usually smell like old gas inside. read the label on any fuel pump at any fuel filling location and it will say something about the vapors being cancer causing. the tank needs to vent and it is the cap doing that for you right outside the window. there are multiple places for a leak to happen. if it is an s10 frame swap then why not just use the stock s10 tank and be done. the tank also comes with a built in fuel pump. the stock tire location is still available then as well. sure, you will need to fab a fuel filler. just like jodoh says and he should know, it's like a job for him, building AD trucks sitting on s10 frames. he has it down to a science and knows what works and what doesn't.
your truck and your decision so you do what you want. be safe though and think about future changes and what you may want down the road.
safest place for a tank, in my opinion, is mid-frame on the inside of the frame rail. can't be all bad if a lot of newer trucks are built that way. safe from front or rear impact and also pretty safe from side impact on the side the tank sits on. I am sure there is a youtube out there that will contradict, there always is. yes, you will have to do some different things for cross members and exhaust routing and also fab a tank filling method but still, likely the safest option and you can still run it down the track if you want to.