recommended oil for '68 383 ?

Dave NEO said
hydraulic flat tappet..my operating temp range is 40F to 90F. NO clue what is in there now but 700 mi after rebuild I wonder what is best as I look to end driving season and maybe do an oil change..

AMSOIL Z-Rod synthetic is available in 10w30 and 20w50 with 1400 zddp. I have used Rotella T but it is changing from 1100 to 800 zddp.