Mike...a T37 in good condition is an 80-100k boat. Anything listed for less than that will need a lot of work IMHO. You will find the T37 quite small and cramped compared to the Catalina...but that is the trade-off for seaworthiness.
As to Catalina36's...you've gotten good advice here and I am also a fan of the boats for their purpose. One thing I have only seen brushed upon for bluewater use is that the hull has a LOT of flex to it as the seas get heavier. This means that on long passages, the hull and things attached to it like bulkheads and hull deck joint will get flexed extensively which will leads to a lot of wear and tear and possible failures. I don't think you can "upgrade" out of that problem.