I'm a dremel addict ... would have put small grinding bit in and elongated the slots ... then feeling guilty I would have used a fender washer to spread contact area. A hack saw would have been too crude ... but hey.
on 526 the slot was maxed out perhaps a touch short, but we did nothing.
If I remember correctly that base beam is not solid ... guessing 3/4+ in. fiberglass with embedded SS plate. since the screws were SS. I think you actually can get your hand under it or at least look at it with a small mirror from the access plate in front of the head.