Now this is just my opinion and many will not necessarily agree but it is based on a short ownership experience with a JPS suby powered car.
My opinion is that while the suby power is nice nothing wrong with it I don't think it's essential to have a really nice car. If you could compare my Suby coupe say to Paul Mossbergs IM (with an air cooled engine) the difference in performance is not that significant (in my opinion) so what I am suggesting is if money requires a compromise I believe a well sorted air cooled car might be a lot more satisfactory over compromising other aspects of the car in order to obtain the suby engine for the same money.
I've got a pretty good idea as to what I think would be a perfect replica 356 and it probably would include a suby engine but the entry fee would be pretty steep. AND when you get in to the $50K and up numbers for these cars and we all know you can get as much or more then $75K in them are they really worth that kind of green.
What I am suggesting is a nice used air cooled car might very well float your boat. It would mine after owning the JPS coupe. Oh and if you are considering a water cooled car I believe Beck as a better set up for the radiator (among other things)
My opinion based on my individual and somewhat limited experience. Me? If the madness returns it will be a used air cooled Beck or IM. Something owned and sorted by a knowledgeable owner. Or one purchased thru Beck or IM. That's what I'd do. (today tomorrow who knows) I believe you can find a very nice car for between $25K and $35K and that's enough maybe $40 couple K if you're talking IM's I personally question whether any replica can justify $75K and up. Notice I said question. For some it's a given and that's OK, just my opinion to consider for what it's worth.
Just to add. The difference in power is noticed at the high end of the performance curve. These cars are not (again in my opinion) at their best pushed to the limits. If you want a high performance experienced I'd suggest a modern porsche not the replica's. Now don't get me wrong they are a fun drive but I just don't think they should be expected to handle power plants in excess of 100 hp. (My opinion) If you want to run with the big dogs buy a Cayman (similar money)