M117 guide rails: Replacing aluminum-backed style w/plastic

[Tomguy]

I have the aluminum-backed guide rails - I assume they are original
I want to put the plastic ones in - at least for the time being - to see if it helps my stretch indicated.

The top retainer bolt seems fine - fits in there well - but the bottom one seems way too loose! The hole on the guide rail is an oval shape, not perfectly round - looks like the Bristol racetrack or something.

Is this right? Wrong? I have other bolts from an engine that had (other) plastic rails in it - the rails seemed snug in that head, but they dont fit in this rail either, the only difference from mine is that they dont have the groove for the spring-wire to center the old-style rail.