They are out there but they arent that common. Most V8 trucks had the big heavy cast iron tranny behind their engines. I was lucky enough to nab one from a member here years ago and I'm putting it to use in my '86 stepside project behind a 318 and in front of a cast iron A-833OD

Your best bet is to find a standard one and either have the hole milled out for the A-833 bearing retainer or have your bearing retainer (the big round thing that bolts to the front of your tranny with 4 bolts) turned down.

I'm not sure about bearing retainer specs, hopefully someone else can chime in with those soon.