<VV> LM Wheels, back spacing differ on size?

[John Sconiers]

Hi,

I currently own a set of 14" and 15" wheels for a LM Corvair.  They are both 5 lug 4.75 bolt pattern with 4" back spacing.  I'd like to purchase a pair of 17"x7" and know I'll still need the same bolt pattern but wondering about the back spacing.  Will the same back spacing work?  What if I went with 18"x7" on the rear and 17"x7" on the front?  Would the 18" back spacing be different?  Can anybody give me specs on a personal car that has a simular setup? Thanks in advance!

JOHN