The heavy case would be the more desired engine. I am not sure which are available for the 336 in a certified category. I know that there were a lot of light cases (original) from 337's that had crack issues so it would only make sense to source a heavy case if it can be used in a 336. The crankshaft differences were mandated by AD's for a lot of Continental Engines. I would think by now most of the original cranks are long gone and all the salvageable units would be VAR. Again why put all the money into an engine and not have the best components. There may be some original 336 engines out there but I don't think you would want to rebuild them if they were light case. The VAR cranks are going to be standard as most shops are not going to chance the liability.
Using the search engine on this message board I entered "crankshaft"
http://www.337skymaster.com/messages...ght=Crankshaft
http://www.337skymaster.com/messages...ght=Crankshaft