My JD has a sliding rod that goes through an eyebolt, but it's practically useless except in the full down FEL position.
The JD bucket has a flat area on the top that is parallel to the base and that is what I use for leveling.
I'd suggest loosening a bolt or installing a machine screw, and then make an indicator out of coat hangar wire. Level wire - level bucket.
Or use a welding rod of bigger diameter and paint it orange (an ugly color).
I really like the level indicator on my NH loader. The pictures attached show a rod that has a "kink" in it (green arrow). When that kink aligns with the bracket shown with the red arrow, the bucket is level. The bracket is just clamped to the roll cylinder with a U-bolt and can be adjusted up and down. The rod attaches to a hole in the dump lever mechanism on the bucket as shown in the second picture. Since you can clearly see the whole rod from the operator's platform, you could paint this rod with indicator bands to your heart's desire. I haven't seen a level indicator I like better than this.
kubota 4610, kubota 4200, JD 455, Toro 256E zero turn mower, Case 135 excavator, hydraulic dumpcart
I have a piece of flat steel on top of my bucket that is parallel to the bottom or the bucket. That works very well for leveling my bucket ... most of the time
The only problem with most of the level indicators is that the only time the bucket is actually level is when the tractor is on level ground. The rest of the time it's just keeping the bucket parallel to what ever slope the tractor is on.
My cheap homemade indicator shows me if the bucket is level no matter what slope the tractor is on. When the pin and pointer are lined up I'm level. So far I haven"t bent it or knocked it off "yet".