[Daryles]

I like Lucas Red and Tacky grease.
I watched a YouTube video testing various greases under different harsh conditions and Lucas came out on top every time.
Buy a "Lock & Lube" grease gun fitting. Very handy.

When you are installing the new bolts you want to install them with the grease passage at 3 o'clock or 9 o'clock. This ensures when you pump grease in, the passage is not blocked by the spring.
With weight on wheels, make a note of the position of the shackles and bolts. Mark a line horizontally with a sharpie across the shackles and bolt head. Take a picture.
When you jack up your rig, the shackles will flip as the weight comes off the wheels/axles. Note the new position of the line you drew. Take a picture.
When you install the new bolts, align the grease passage with the line on the Shackle.
When you put the wheels back on the ground the shackles should flip back to their normal weight on wheels position the line should be horizontal and the grease passage in the bolts should be at 3 or 9 o'clock.