On my Astro build I found a shop the will build a Ford 9" exactly to the one of a kind Astro offset and copy the mounting.It is a alloy axle with a nodular center where you add your gears and posi with any bolt pattern you want.The shop's name is Spraker Racing in Schenectady,NY.Oh you have a choice of a 28 or 31 spline.Just got to provide them with a copy of stock Astro rear end.PM me if you want their phone number.I do think the price was in the range of $1,200 bucks which is a pretty good deal.