[Billy Nees]

CYLINDER HEADS
Must be correct casting number for year and horsepower
claimed, per NHRA Technical Bulletins or NHRA accepted.
Porting, polishing, welding, epoxying and acid-porting
prohibited. Combustion-chamber modifications prohibited.
Cylinder heads are additionally restricted in that they must
retain original-size valves at original angles +/- 1 degree
and must be able to hold original cylinder-head volume per
NHRA Specifications. Runner volumes may not exceed
the current Super Stock cylinder-head volumes as listed
on NHRARacer.com. Regardless of the poured volume
measurement, any modifications to intake or exhaust runners
prohibited. Any evidence of modifications from the original
castings will be grounds for disqualifications as determined by
NHRA in NHRA?s sole and absolute discretion. Any aftermarket
steel valve permitted, must retain stock head and stem
diameters. Only engines OEM-equipped with sodium-filled
valves may use sodium-filled replacement valves. Titanium
prohibited except OEM. Hardened keepers permitted. Lash
caps prohibited. Valve-diameter tolerance: +.005-inch or -.015-
inch from NHRA Specs. The following are prohibited: spark-
plug adapters; any grinding in ports or combustion chambers;
removal of any flashings; sandblasting or any other modification
to cylinder head; any film coating of intake and exhaust
runners; any film coating of combustion chamber. Runners
and combustion chamber must retain OEM appearance. Final
Stock Cars Section 11A, page 4STK
acceptance as determined by NHRA in NHRA?s sole and
absolute discretion. External modifications prohibited. Intake
side of head may not be cut into any part of valve cover bolt
holes. Valve-cover bolt holes must remain unaltered and in
their original location. Intake manifold bolt holes must remain
unaltered in their original location. Heat riser passage may be
blocked from intake manifold side of cylinder head. Blocking
passage down in valve pocket prohibited. The following are
permitted: polylocks, jam nuts, screw-in larger-diameter rocker
studs or pinned studs, bronze-wall valve guides, cylinder head
studs. Valve spring umbrellas optional. Cylinder head may have
all of the seats replaced. Any valve job permitted, O-ringing
prohibited. Exhaust plates prohibited.

This is off of TODAY'S NHRA Rules page and as far as I can see, there is no rule revision.