Not sure about tapping and using the bolts, mine seemed a little too big
here was my solution -
I wound up buying various sizes and lengths of the "plastite" screws from McMaster-Carr. I wound up using 5/8 length and I think the #8, I also got #6 but they seemed a little small.
https://www.mcmaster.com/92295A209
I also probably should have gotten a little longer if they had it, however it did seem to hold
as far as the rivets, I still had some stainless ones from another project so I used them, however I have read where other have just screwed that cap back on.
Overall it was a success, have only had 1 trip but it has worked several times in/out with no problem. Had to do adjustments on the setpoints of the motor so it would extend/retract the right amount.