I have a 87 f250 4x4 with a 5.0, my y pipe is rusted away and I need a replacement, trouble is I can't find one for a f250 w/ a 305, could I use one from a f150?

 

There are differences in the exhaust on the 1/2 ton compared to the HD trucks, the cat is separate on the HD while they are integrated on the 1/2 ton, and the smog tube connections are different. If you can handle some exhaust mods the 1/2 ton Y pipe will work.

 

Imo the light duty y pipe with 2 cats (which is what you probably have in your light duty 2fiddy) isn't worth putting on there. But, if you have one to replace the old, by all means. Be sure to core the factory cats, they're actually worth a good chunk of beer money.