help with wheel ofset

i am thinking alot right now my hoosier tires seems to be very difficult to get from my speedshops suplier in your country so i am looking for a new tire+wheel combination,
right now i have 6½x14" rims with 1/4" negativ offset and the tires measure 26x11"
its realy hard to find 14" tires with traction so i am looking for 15"wheels and i am not sure if the wheels i have found should be ok old tires have rubbed the leafsprings a litle so iam trying to fix that problem to.

http://www.ultrawheel.com/pdf/rims/061.pdf.pdf
part# 61-5865k
that is the 15x8" rims i dont mind if the tires look a litle baggy on the sides so i could live with 15x7" wheels to..
would that wheel be any good or are my math to bad? i want to use a tire aproximatly 27X10½" on 15" rims
does it seem resonable?

car is a duster 73 with stock wheelwells