Prop?....
hmmmmmmm, I dunno on that one. I think trying to mount a prop inside that pump housing might be a tough one. It can probably be done though.
If you'd like to look at an impeller, which requires no mods on your end, we might can help you on that!..........:rofl:
In our parts warehouse, you'll find your impeller for about $88 bucks and the grate for about $70 bucks.
As for your post being in the "mod" section. There isn't a lot you can do to mod the 657, that would be cost effective.