oil change dilemma: '66 C-10 w/ 327

[likaroc13]

hey guys,

since purchasing it, i haven't changed the oil in my truck yet, so i thought this would be a good weekend to do so...however, i don't really know what grade to use though...it is a 327/Powerglide combo with powerpack heads...i have no idea of the current mileage as it's not the original engine...what grade was suggested for the factory 327? or do you have another suggestion? thanks for any help/info