You shouldn’t have to re torque the rockers in a new motor (if adjustable rockers, you may need to re adjust after a bunch of miles, especially if a solid flat tappet cam). My motor has 25-30k on it & I’ve never had the valvecovers off of it (actually as I type this I realize I did once when I had the intake powdercoated - never touched the rockers).
Are they torque to a specific ft lbs? This is not normal on a Gen 1 style SBC.
Most (almost all) chevy motors have lash-adjustable valvetrain (Mark V big blocks do not, but need converted when adding a higher lift cam). If you have to adjust the lash, you will have problems with them loosening again. Do yourself a favor & spend the few $$ on polylocks.