You should run as light a weight as you can that gives a ~15% difference in hot/cold pressure. This will take a little experimentation and will depend on build clearances. 10W-30 may be a good place to start. Just remember - heavier
oil is not better if not needed to maintain pressure. It's counterproductive during the critical cold start time - where much wear occurs.
And semi-
synthetic is a good idea for these old Ford engines as well (vs dino or full
synthetic). I make my own with a mix of 15W-50 Mobil 1 (high ZDDP) and 5W-30 Mobil 5000 (about 2 parts dino to 1 part
synthetic). Kendall GT1 is a fine choice as well. Many other fine choices out there.
BTW -
oil should be changed in the fall for sure in order to get the byproducts of combustion out. Mixed with condensation, they form acids that can etch interior surfaces. Ever wonder why old unused cars often smoke or rattle when recommissioned? You can change again in the spring if you want, but benefits then are minimal if the vehicle has not been started during storage (also not good - as the engine
oil never truly gets warmed up).
Keep us posted on what you choose...