Will this work
 

I have a all stock 1996 s10 blazer 4 door 4x4 I know the stock backspacing is 6" for the stock rims but the rims I want to put on it comes in 2", 3", or 4" backspacing can I use one of those and not have any rub while turning the front wheels if so what's the biggest tire size I can use the rims I want are 15"x8"

the lower the number the more they will stick out , wider stance . I have camaro rims and before I did my body lift they rubbed . then I bought 21/2 inch wheel spacers and they rubbed again , i did the torsion bar tweek and it stopped the rub but I do not like the torsion bar tweek so I took the spacers back off . The spacers have treated me good though , I was worried they might break under heavy wheeling conditions . But I have had no problems with them be sides not being able to see out any of the windows even on a back dirt road . It did make the truck look super bad though .

I was going to get the ones with the 4" backspacing they should stick out about 2" further then the stock ones and I was going to put some 235/75/15 mud terrains on it and I don't want to mess with the torsion bars and the rims I was going to get are the chrome bassett D-holes I found them for $68 a piece

With 4" backspacing an stock size tires there is a chance you might rub the fender when turning. My rims are 4.5" backspacing and in only got about .75" between the tire and rear of the fender when turning. If it does rub, a small t-bar crank will should the issue without any major side affects.

15x7 with 4" BS would stick out 2". Since you said they're 15x8, they will stick out 3" compared to the stock wheels.