I've been lucky with the 4EH's so I stick with them. I have thought about trying a group 51 as I belive they would fit in the original tray and be much closer to original look.
I belive the piece could have fallen into the back section of the casting. My guess to get to it back there would be to pull the pto unit. I do not know if it would be ok in there or it you should get it out.