[Wavytone]

Use the stars.

Can you borrow an Equatorial mount with a decent dec circle, or encoders ?

If so use that... Choosing a bright star near the east or west horizon and use an Astro program to find its declination; lock the dec axis to the stars declination, then adjust azimuth of the mount so you can centre the star in a finder or small scope; this will get you within a fraction of a degree of the dec circle is accurate. This works best for stars with dec between +15 ... -15 degrees.

Once you have the az right set the dev axis horizontal and rotate the scope down to point at your fence (the scope should be pointing due south on one side of the mount) Put a mark on the fence. Flip the scope to the other side of the mount and repeat. These marks provide a ready guide to where south is.

Now plonk the pillow block mount on the pier and align with the marks on the fence.

To set the altitude use a star near the meridian: use any Astro program to show which stars are on the meridian, or use any smartphone app that provides a clinometer.