Update on my Volvo AQ240A/280 over heating problems:

Pulled the manifolds, heat exchanger, and heads last Sunday and took them to
town on Monday.

The exhaust manifolds and risers were in pretty good shape except for some
external rust. They got hot tanked in a 3 dip program and came out in good
shape.

The heat exchanger turned out to be plugged with some seaweed. They hot
tanked it and cleaned out the tubes - they also found a small leak at the
filler neck and fixed that.

By next week, I should have everything back together and running strong.