As loose as those clearances are, I'd go 20W-50 VR-1 in a heart beat
I would not use the Joe Gibbs break-in oil unless you have a roller cam which I see you do ... So that might work out OK. Is the Gibbs oil 20W-50?
On an engine that was not completely engineered to use it, I would never use a full synthetic on start-up, and agree that it should only be considered after three changes. That is also common practice in marine and aviation engine rebuilds.
If you supply more info like spring pressures over the nose, cam type and MFG along with lifter selected, I might change my recommendation - but most likely not. VR-1 is the hands down most popular oil for built engines in a poll I conducted at Chevelles.com (I mostly build BBC's, but the odd SBF now and then...). It's more than 2:1 over the next most favored oil - Mobil1 ... That is with a sample base of over 200 responders. Big enough sample base for the built engine crowd
Unfortunately I can't buy VR-1 any longer in the Komunist Kollective of Kalifornia (KKK), so I have to drive to Reno to get it. And because of that, I am doing a lot of evaluation for built engine start-up oil. On a slightly tighter motor I would use Chevron Delo 15W-30 SD (severe duty), or SAE 30HD. But you are out there a bit, so 20W-50 makes perfect sense. And it's good down to at least freezing (32*F) so I would not sweat seasonal changes
If you have ready access to VR-1, just do it and your motor will be as happy as it can be
After you get say 2,500 miles on it, maybe switch to Mobil1 15W-50. It's also a very good oil