The offset's somewhere around .090" - .100", from memory..don't remember the exact #s. If you have wide journal rods, and a wide journal crank, you can't mess with the big end; you'll have to make clearance at the piston pin boss, either by machining the piston or narrowing the pin end of the rod, or both.
If you have wide journal rods and a narrow journal crank, you can narrow one side of the big end of the rods, and get about half of your offset there (.890" to .847"). Then you may need to do nothing on the pin end, or at most minor clearancing of the piston pin boss. If you narrow the rod on one side, you will probably have to put them on the lathe and re-chamfer the side you narrow. I did this for a set of SBC rods that Nick Micale has; I might have pictures somewhere.
I am running on center rods in a stock block, had to cut the pistons to fit. If you want to know why PM me, as i don't need any more threating comments from a particular vendor.