Once you're in the $39.95 range, why not just get a pre-barbed core from
BeCooling/AquaStealth for $34.99 plus shipping? Yeah, it might end up being a little more expensive, once shipping is factored in, but do you really
like having a tubing size adaptor in line?
I just got one, and it looks as though the shroud was designed for
exactly this core.
I certainly understand going to the auto parts store to get a core, but IMHO, the point of that is getting a core like this for $20 - or building your own unavailable-anywhere-else BigAssedRadiator(tm).
Your other option (again IMHO) is to go to a radiator repair shop, shroud and a couple of pieces of tubing in hand - tell the guy what you're trying to do and how much you want to spend, and for $40 you'll likely end up with a
very nice setup.
I'm surprised that some radiator shop hasn't gone online, specializing in this work - it's much nicer than the usual stuff you have to do there (dealing with dirt and sharp edges in spaces your hands don't fit into, usually crouched down or on your back).