As for the mounting frame bolts, I can't remember what size these were, but when I had to remove them to install the MMM front support brackets, I couldn't find a socket, SAE or Metric, 6 point or 12 point, of any size that actually fit them. I had to beat the closest impact socket I could find on with a hammer to get it on there far enough to engage the bolt head.
I think it turned out to be a 5/8.
And, they were TIGHT. It took everything I had pulling on an 18 inch breaker bar, with both feet on the rear axle to get them loose.