Hardened eye bolts?

"For other than vertical loads, general practice is to use 60% of the safe working load factor for a load 30 degree from vertical; 33% of the vertical safe load 45 degree from vertical; and 20% of vertical safeload for load 90 degree from vertical". Don't know if this will apply to your app. or not. They also showed 5/8" Swing Bolts in a 4" lenght with a 5/8 hole of heat treated steel, black oxide finish 1036 @ $9.19 each.
Depending on the app. Safety Engineered Hoist Rings or Heavy-Duty Forged Lifting Bail Hoist Rings may be the ticket if one could find or modifly the bolt lenght.

The Armstrong brand from the same source was about double the price. I used to work at Armstrong. Their eye bolts and all other eye bolts made in U.S.A. were for all practical purposes identical as they all met the same industry specifications and since OSHA is watching every move, none of the U.S.A. ones varied much from published specifications.

By a forged one and its probably better to buy one made in U.S.A.

Check J&L Industial Supply, MSC, McMaster Carr and the likes. All have websites and all will have regular forged eyebolts that will fit your needs.

If you are unsure as to the strength you need, go to a larger size than what you think you need. The cost is reasonable for the extra insurance. Should you happen to exceed the limits, the eye bolt will stretch and usually well in advance of failure.