Ignacio,
I'd forego even considering the 336 because you'll definitely be rewarded with faster cruise speeds with the 337. Also, you'll find refinements in the airframe and engines throughout the model years as the product went to its close in 1980. In my personal estimation, based on those refinements, I'd go for the latest model year your pocketbook can afford. And buy one with as nearest the compliment of radios and options as possible, because if you start adding stuff afterwards, it gets expensive very quickly. Typically the older 337's, if they haven't been updated, will have an assortment of gyros and radios that will have to be replaced, plus some early models had AD's that the later ones don't... an important consideration.
Since you're down in Florida, you might check on a 1977 normally aspirated 337 I've seen advertised on The Controller website...
http://www.aircraft.com/listings/for...D=1042088&nh=0
Here's the basic info:
S/N: 337-01790, N-53696, 8263 TT, 1384 SMOH / 926 SMOH, IFR, Aircraft ready to go. Great Interior and Exterior. RG International (305)871-3471 (305)876-9540
Seems I recall seeing a $60K price tag, and considering model year and the equipment, later Narco avionics, not a bad airplane to possibly consider. Maybe ask for some help from folks who live near your area and who frequent this board that could assist you with looking at this one, as you don't want to buy a pig-in-a-poke. I know Ernie Martin and Bob Cook don't live too far from you and could possibly drop in for an eyeball.
SkyKing