We were really fortunate that the prior owners of Over Easy had done a great job of keeping the original boat papers and manuals!
For reference only:
* The original empty weight for a 26X was listed as 2350 lbs (Note1 & 2)
* The original Macgregor trailer weight was listed as 710 lbs
** The original combined 26X & trailer weight combined 3060 lbs
Note 1: This does not appear to account for any engine, fuel or accessories.
Note 2: We assume though that the empty weight listed would have included the weight of the baseline original mast, boom, rigging, and sails.
As was mentioned things change over time and there are always other variability aspects to account for.
As such we are going to be offloading what we can from the boat and also minimizing what we carry in the van.
The towing specialists agree that a tongue weight of between 7% to 10% of the trailered load is the target but to avoid going too much. If the trailered load isn't stable within that range there is something amiss that needs to be addressed. (Too light will definitely lead to fishtail oscillations and too heavy can unnecessarily/excessively load the tow vehicle's rear suspension as was mentioned. Sort of a Goldilocks aspect to get the tongue loaded enough but not too much.

.)
So far all our numbers are adding up within the various capacity


recommendations.

So far so good!
I appreciate the suggestion of the "load divider" board. Especially the photo with the bevel edge vertical transfer board to make it easier to locate it accurately. My Dad had done a similar set-up when I was a growing up to measure the tongue weight for our travel trailer. (He liked wood working and had a hardwood set with a double bevel for the vertical and a pair of double bevel lower transfer fixed and scale pivot blocks. He used to check everything before just about every trip we went on which was a great way to learn the functional math as a kid. It was actually a fun routine.)
If we can get to some weigh scales we will also get that done as well. Unfortunately there do not appear to be any locally that we have found but it is something we would like to get accomplished before our trip.