sorry what do you mean it didn't have any water in the car??
I hope you don't mean water in the coolant system. You CANNOT run the engine dry.
The cylinders (which are surrounded by water channels) will melt in no time.
Also you should have primed the carbs and lines before starting and checked what kind of oil to use.
You left old oil in the car? I'm confused and concerned about how you are doing this.
Rotor should have been cleaned and checked before starting also.
Engine preparation before starting is ESSENTIAL, water, oil priming etc.
I use 20w/60 oil. Pressure is good and no issues with hydraulic tappets. If your pressure is good with 15w/50 then go for that. The thinner the better as long as you have the correct pressure.
If the pressure is too low, the tappets will bleed out and not work properly and too thick also is not good.
All depends on the condition of your engine, crank clearances, pump condition etc.
Try 15w/50 first with a good oil pressure gauge and go from there.
If the engine has not been thoroughly cleaned do not use synthetic, semi would be a good choice (70% mineral).