Mounting up top is two P-clips. They are far more solid than the lower mounts, grabbing and shaking doesn't budge them. Arms are mounted on the inside side of the seatstays, I couldn't get them on the outside. Adjustment bolts on the rack are all solid and secured.

Thanks for all the input! I'm also leaning more towards the rack itself, but the loose bolts do cause me concern that I want to sort out. Maybe I'll try looking at some SAE bolts, seeing if any of them fit a bit better, but otherwise I think I'll tap it. I'm also thinking that a front rack will be added, just to get some weight off the back to help with handling, that was always in the plans anyways.

Any advice on a bit sturdier rack? Also, is it wrong to think that anything marketed for a 700 would also fit a 27"? Can't imagine there is enough of a difference in tire size to run into any fit issues.