Help with oil type and weight selection

for your car and climate 20w50 would be best but of course it needs to be changed more often because its conventional. I usually recommend 0w40 but not in your case as you state its not a daily drive, its would be more expensive and not necessarily better.
What 20W-50 has demonstrated performance through a demanding manufacturer approval like most 0W-40 oils?
In my customers cars, vintage and semi-vintage performance cars, both supercharged and NA, I use Mobil 1 0w-40 or Mobil 1 15w-50 depending on the climate and season. For your case I’d use the Mobil 1 0w-40 and change it as often is indicated based on the results of a Blackstone Lab report.

Both of those oils have excellent wear protection. In fact on my personal ‘66 supercharged Shelby GT-350 l have zero measurable wear after 88,000 miles.

I’m also using the 0w-40 in my daily driver, a 2002 Jaguar XKR (also factory supercharged). The Mobil products are so inexpensive I don’t see a legitimate reason for going with a conventional oil.

For your climate and usage 10w-40 changed every year (or two). Checking with the engine builder may, or may not, be a good idea. Some haven't a clue about oil and some are very well educated. Syn or Conv is your choice and probably has no benefit. Most Conv are a syn blend now.