What's the point of them? They'd only be needed if you were using a stud-girdle which requires taller rocker covers.
The L29 doesn't have enough valve spring pressure to need stud girdles.
No stud girdles, no taller covers...no need for spacers on the plenum.
IF (big IF) I were upgrading the heads to allow enough RPM to need really-stiff valve springs that needed a stud girdle to stabilize 'em...I wouldn't be using that intake manifold.
The L29 doesn't have enough valve spring pressure to need stud girdles.
No stud girdles, no taller covers...no need for spacers on the plenum.
IF (big IF) I were upgrading the heads to allow enough RPM to need really-stiff valve springs that needed a stud girdle to stabilize 'em...I wouldn't be using that intake manifold.