The installation instructions below are from Hammer's website for the most part.
They also have an Installation Video for the billet bases.

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Installing the billet pushrod bases:

• The undersides of the billet bases are dimensionally the same as the factory pot-metal rings.
• Hammer's website suggests to install two pushrod tubes into each base at the same time.
  This can be done but it may be easier for some to do them one at a time.
  Installing two at the same time takes unnecessary pressure to push the base down the tubes.
  Both tubes have be lined up very straight or the base hangs up without going down without further pressure.
  (their installation video also mentions you can do one at a time)

• With the heads installed, put the upper O-rings into their pockets in the undersides of the heads.

Lube inside of O-rings with a little grease or oil. 3)

• Remove the roll pins in the case deck that are used to align the factory bases.
• You can pull them out with a pair of pliers or vise grips.
• They come out easily if you clamp them, turn them left and right to loosen them and then lift up.

Be careful not to scratch the case while removing the pins. 4)

• You can place a flat piece of metal on the case to protect it while maneuvering the pins.

If the pins are tight, you can use a pair of vise grips to clamp them. (that way you don't slip off the pin onto the case by accident) 5)

• Clean the case deck and make sure the deck is free of debris or scratches.
• Clean any grease or oil residue from the underside of the billet base.
  • This is especially important in the areas where the seal will be contacting it.
  • Use brake parts cleaner or a similar solvent and wipe with a paper towel.
• Clean the seal in the same manner in all areas where it will contact the billet base.
• Put two seals into position in the underside of a billet base (the seals will normally hold up in the base by themselves).
  • You can put a few drops of super glue onto each seal to help hold them in place in the base if you choose.
    (but this generally isn't necessary if you've got both squeaky clean).
• Lightly oil the pushrod tube in the middle where the larger OD starts.

Everything needs to be squeaky clean so the seals don't slide out of the base. 6)	The seals fit snug in the base. 7)	This oil will get squeegeed down by the seal. 8)

• Stand up both pushrod covers side by side.
  • Obviously just one if you're doing it that way.
• Carefully slide the base and seal assembly over the tops of the pushrod covers.
• Push them down the covers, over the thick part of the covers, and down to about an inch from the bottom.
  ( make sure you don't dump the seals off the end of the tubes)
• Now, make sure the seals are still in place in the underside of the billet base.

1. Carefully insert the tops of the pushrod covers up into the O-rings in the head at an angle.
   • Be careful not to cut or damage the seals with the lip on the tubes.
2. Swing the bottom of the assembly into place over the lifters.
3. Push the base down onto the case deck and hold pressure on the base with one hand.
4. Without releasing pressure on the base, install both screws and snug them down.
   • Once they're snugged down you can let go of the base and finish tightening the screws.
   • The key is to never let the seal pop out of the bottom of the billet base.
   • If it pops out during this process, it'll get sandwiched between the base and the case deck and you'll have a leak.
   • As long as the seals stay in place, they will seal just fine.
5. Repeat the process for the other cylinder.