Brian, I have a couple of thoughts after having built a very similar engine to the one you're doing.
The Vintage Speed exhaust is great looking, simulates the big-sausage 356 mufflers and like you, I thought the Super Flow was the way to go since it's going on a "big" motor. Just know that it's loud, and in these open cars, as you know, that volume which some love, can get old.
I was at a large 356 gathering last weekend and most there had stock exhausts, most had driven long miles to get there and though their exhaust notes were quiet, they had that confident sound that says: "Don't worry, I can still blow your doors off!"
I think 44's can be made to "work" on your engine and many, if not most builders claim they are the "way to go" but why push-the-river?
If you want, as I did/do, a grocery-getter, a back-road cruiser, a car with lots of low-end (think: around-town) response, I urge you to insist on 40's. They are sized for drivability on an engine of your size. the higher air-speed through the smaller throats equals better carburetor and engine response. Yes, you'll lose some top-end power (think 5,000 rpms and up), but who cares? I sure don't!
I'm heading out to my buddy: Jim Ansites this morning to try one last time to get my 44's working and if we can't, which is most likely, we're putting on a set of 40's, I'm just tired, after 9 months of swimming upstream, to get these stinking 44's right.
OK, tirade over, boy do I feel better!