5W30 in my non roller 289.  You could use 10W30 or 5W30 and be fine.  The grading system for oil that existed when these engines were new no longer exists.  If you try to cross it over to a modern spec it will give you 10W30, but I found that had my oil pressure higher than I'd like so I switched to 5W30 and found that more reasonable.  Working the oil pump too hard just wastes power and efficiency.  I hold a steady 25psi at warm idle now and jump up to 60psi at WOT at 5,000RPM, which is where I shift when running it to max RPM.  You really only need 10psi per 1,000RPM in an engine with an efficient oiling system, which the SBF has.  Now I can't say for FE or I6 engines or other older designs.

I use Walmart brand 10W30 - 5W - 30.....unless somebody has oil on sale,      then I would buy that!
IMHO.....it all comes outta da same hole!
6sal6

Ron68 wrote:

I use 10W-30 in my non roller 351W, and I also include a bottle of ZDDP additive to every oil change, as the newer formulated oils no longer contain zinc.

Thanks Ron, I forgot to mention that.  I put a bottle of STP in every oil change because it has the proper level of ZDDP in it.  You absolutely need this for flat tappet cams.  Don't use Diesel oil.  There are a lot of old posts claiming to just run a Diesel spec oil because it has more zinc.  That's no longer true, and hasn't been true in over 10 years.  They took the zinc out of the Diesel oil eventually as well. 

On a fresh engine I would run synthetic or a blend without concern.  If its an older engine I would stick with regular conventional oil.  I've had issues over the years with synthetic added to high mileage or older engines causing seal leaks that weren't there before.