Mach One wheels and offset

Hi, I have a 1998 300tdi which I'm fettling bit by bit. 40mm lift using TF and Procomp parts. I have a set of Mach One steels to replace the Boosts, and whilst I'm happy to do a rear-arch 'Camel Cut', shaving the rear doors will result in a whole world of pain for me ( it's Madam's car, after all). I have a new set of 265/75R16 BFG MTs, which I've decided against fitting because they will be 'Just Too Big'. Looking at the comprehensive tyre-size sticky at Disco Tire Fitting Guide the 245/75s seem to be the biggest that fit my particular needs. However, it makes no mention of offset, which will obviously affect things a bit. I measured the offset on the Machs, and the distance from the hub-mounting to the front of the wheel is 10cm, and the distance to the back of the wheel is 12cm. Could someone with a bare Boost alloy (or with the answer to hand, of course) tell me if my Machs are more offset than the Boosts, and if any further mods will be needed. TIA