I know I'm gonna have to grind some, but I don't know how to figure out the whole offset/backspacing thing.

They are some pacer 15x10 wheels with a -38 offset and 4" backspacing.

 

anyone have any idea??

 

goto Discount Tire and do a test fit

There was a thread a while back about grinding the rears for 15's to fit

 

I know they will fit over the calipers but I don't know how to check offset and/or backspaing to see if they will hit the banjo bolt on the caliper.

That is the only thing I'm worried about.

 

15x10 with 4" bs are gonna stick out like a bitch.
it won't even be worth it since you'll be out the contact patch of the other cars laying down rubber.
with that bs you wont even come close to the bango bolt.
(stock bs is 5.2" and there is still 1" between rim and the bolt)

mine are 15x8 with 4" bs.

 

Will some 27x10x15s work well on a 15x8 rim?

 

yeah.
27x10.5x15 is what's on my truck in the picture.
my friend is letting me borrow them to see if they hook up before buying me some 28" tall full slicks or drag radials.

 

What is the offset of your wheels?? Would some 15x8 with a 4.75 backspacing and +6mm offset, put me in the contact patch better?

 

-11
yes that would put you with a better contact patch.
use this---> http://www.wheelsmaster.com/rt_specs.jsp