The only variance you will see is deflection in the measuring instrument. One thing that can throw you off is the bearing retainer hole not being perfectly round. That is one of the issues with older lakewood bells along with the horrific alignment problem.
My quicktime bell has a litany of issues that required correction. I have used it on a few different engine and none required more than .014 offset dowels whereas the lakewoods use mostly .024's or whatever Rob sells.
I keep a set of each in stock if that is a good indicator of importance.
My advice is to verify the retainer hole to see if it is concentric and mark any anomalies so you can account for them.
If you need more offset than rob dowels offer you can get an adjustable reamer to slightly open up the alignment holes. At that point you can weld locating washers in place to retain your position.
