lewm
you are absolutely right about proper alignment. I have the tools and experience, I will be especially careful and re-check the longer arm setup. Like construction, measure twice, cut once.
I just bought some modern tools, goodbye Shure Sea-Saw tracking force guage, hello digital scale,
https://www.amazon.com/gp/product/B01N9TRSPC/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1
hello clear plexi block with 2mm grid,
https://www.amazon.com/gp/product/B07794JXYZ/ref=ppx_yo_dt_b_asin_title_o07_s00?ie=UTF8&psc=1
hello new alignment disc (asked sister-in-law to give it to me for Christmas). I like that it is the thickness of an LP. I don't need the strobe on the other side, but, a confirmation, and when I help others ...
https://www.amazon.com/dp/B07PH37HWP/ref=sspa_dk_hqp_detail_aax_0?spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExVTQzSDhOUThNS0EyJmVuY3J5cHRlZElkPUEwNjY1MDI1OVdUU0MzS0k5V1ZRJmVuY3J5cHRlZEFkSWQ9QTA5OTI2MjcyNTBJWEI0TkkwNzZBJndpZGdldE5hbWU9c3BfaHFwX3NoYXJlZCZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU&th=1
Now I use a 1/8" thick mirror for front view as it 'doubles' any misalignment in the reflection, perhaps I will glue a thin mirror foil onto the alignment disc somewhere.
The older you get, the harder it is to put a shim in one side if needed, and tighten those 2 screws.