Hi Jack,
Although there are changes in plane and elevation it is not as convoluted as it first appears but there is no direct through passage without going through the bell housing connecting opening.....therefore you can not blow through from either side without dumping the crap in the bell housing/main engine passage so long as the pony is mounted.

O.M., thanks for the picture. That's the only picture I've ever seen of the bottom of the pony and it tells me a lot.

Actually my plan was to pressure the main engine and use air to break up the crud, hoping to flush it out through the pony block holes. May not work, but if it does it could save me a bunch of work and time. It'll be messy but I've flushed some pretty bad ones with air bubbles and made it work.

The diesel had some crud in the back of the block and I cleaned it up a couple years ago with cold water flush and air. I just didn't think about the pony because it sets a little above the back water jacket sump. I'm betting it's not scaled up too bad because I run Cat conditioner and we have very little mineral in our water. I'm betting it's just crud.

Thanks for all your help.

Jack