360 crate timing

having a lil troble gettin it set right. idle is ok, under load is ok, cruising at 60 plus i have a lil stumble, any suggestions? when I advanced it to about thirty four , thirty five @ three thousand rpm it gor worse, so what should I retard it to. Im guessin thirty, thirty one. Any one have experience with this motor, I guess I just gotta find the sweetspot. Thanks