Recommendations on replacement radiators?

[Dr.Jeff]

the way the fins are attached to the tubes these days

Referred to as "high efficiency" cores. The fins are thinner, more tightly packed together, and have more 'waves' in them. All this increases the surface area.

 

[dllubin]

Referred to as "high efficiency" cores. The fins are thinner, more tightly packed together, and have more 'waves' in them. All this increases the surface area.

I think you quoted him almost directly!

 

[dllubin]

The old radiator guy works fast. He promised me the radiator end of day Friday, but he called me at 9AM on Thursday to tell me it was done. Here is a closeup of the copper core and fins: