spdrac,
I feel that you know this already, But you have to build a rear sump pan to make this work. Ford did not make one and the pan rails on the 250 are wider than the 170.
I started down this road before I found my 89 SC Engine.
I have all the 170 sump parts and a 69 Mav 250 engine for sale...
Here is a pic of a 250 rear sump pan that someone (unknown) built.
...JJG