Thanks for the recursive post.

It's going to be hard to put any more radiator in there... I already have tried, as noted, a 3-row copper/brass 26" and a new aluminum 3-row 26". Any thicker core would not leave enough room for a fan! It's a tight squeeze as is... any radiator recommendations if this proves otherwise unfixable?

Regarding airflow, the radiator is just sitting there behind the grill, basically open to the incoming air. I recently posted that I completely removed the fan/shroud assembly completely, and still had temps well above the t-stat opening when driving at 30 mph. Would ducting really be necessary or helpful? In your experience, at what speed does the fan stop contributing? Is 30 mph not enough?

Yep, I know the difference between thermocouple types. I've used K-type to measure EGT's. I'll double check my gauge in boiling water since I won't (hopefully) be measuring temps over 210 anyway

Lower hose with the old radiator could not possibly collapse (two short silicone elbows and a rigid 2" aluminum tube connecting them). Identical temp behavior with the new rad and a parts-store Gates hose. But that's definitely a good zebra to look for