Chevy 350 V8 To Chevy Inline 6 Swap ASAP

[GMC85HighSierra]

Hello, I am looking at swapping out my 350 for a Inline 6, but I have some questions. It would be going in a 1975 Chevy K5 Blazer. Looking at information first to see if I want to buy an inline 6 for my truck.

-How good of an engine is an inline 6 compared to a 350?
-Is a 350 trans a good mate for an inline 6? If not, what automatic transmission do you recommend?
-Where does the motor mount up? What do the brackets look like?
-Are the 250 and 292 the best 2 inline 6's to look for?
-Do inline 6's get better gas mileage than a 350?

Would like to know this information as soon as possible. Thanks