The modified MP T-6 chain tool seems to have worked! A few notes in case it helps someone else.
To press the plate onto the master link (before riveting) we just used the T-6 tool as it was intended -- with the slotted back plate.
When riveting, to hold the pin on the backside we put a strong piece of metal, a chain plate from one of the links we removed. We tried the backing plates/anvils that come with the chain tool first but they were too weak in a variety of ways.
To compare the distance between plates on the master link vs other links and then again to compare the diameter of each pin head after riveting to make sure they were flared enough, we used small locking pliers in place of calipers. We locked them closed and then used the screw to adjust the distance between jaws. No good for measuring but pretty damned good for comparing.
Thanks again all. We're back on the road, to Samarkand tomorrow.
Si and Jeff