I would not use that oil for that application in the Texas summer heat.
M1 15W-50, M1 V twin 20W-50, GC, Rotella T6, M1 0W-40, M1 Delvac 1300, would be my choices for the kind of heat Texas has.
If you want to go with low cost then Rotella T5 15W-40 would be a good oil.
You could probably use 5W-20 for winter Texas temperature, but starting off with a 20 for the top number is thin, even for 75 to 50 ambinet temps.
One of the things you should keep in mind is that most chemicla reactions double or half for every 10 degree C, or 18 degree F.
Keeping that in mind, think of oil as loosing half of its Viscosity for every increase of 18 degree F. The oil in an air cooled engine druing a normal use will probably reach 212 F if the ambient is 75 F. At 212 F most 30 weight (upper number) thin out to a 10 weight. And this is what your engien is designed to run at. If you are going to run that engine in Texas summer heat, you will require an oil that is above 30 weight to start with so when it is heated above 212 F it does not thin to something less than 10.
If you start with a 20 as the top number, you already lost the battle to keep your engine properly protected, because it will thin to less than 10 at 212 F when the engine is up to full operating temperature at 75 ambient.