SS/CS question.

[SSDiv6]

Originally Posted by Glenn Briglio

Only available in a truck. Rules state passenger car only.

Passenger car engine rule only applies to regular Super Stock and Super Stock GT.
For Modified Class, just needs NHRA Approval of the cylinder head just like all the other aftermarket heads approved for Modified class.

CYLINDER HEADS
V-8 splayed valve permitted in AS, canted or inline in BS,
inline only in CS, and any valve configuration in DS. All heads
must be NHRA-accepted, two valves per cylinder, except
in classes DS, ES, FS, and GS, four valves per cylinder
permitted. Aftermarket aluminum (no billet) cylinder heads
permitted except in CS. Angle milling and/or rolling permitted.
Aftermarket iron heads permitted in CS. Porting, polishing
permitted; header plates permitted. Exhaust port plates
that protrude into port prohibited. Any valve size permitted,
valves may be tilted and/or canted. Combustion-chamber
modifications permitted. The valve cover rail may be modified.
Heads may be cut for larger pushrods and valve springs.
External modifications permitted in port area except for
SS/CS. Spark plug holes must be in NHRA-approved location.

The Superceeded Parts rule does not apply to SS/Modified either.

ENGINE
OEM aftermarket small-block Chevrolet (SBC) engines with bore
centers greater than 4.420 inches are not permitted. Engine
must be same corporate make as body, naturally aspirated.
Displacement unlimited in AS, limited to 366-cid originalproduction
in BS and CS. Engine setback or raising engine
prohibited. Motor plates and mid-mounts permitted. Timing-belt
covers optional. Harmonic balancer meeting SFI Spec 18.1
mandatory. In Section 9A, Connecting Rods, Gaskets, Intake
Manifold, Oil Pan, Pistons, Superseded/Replacement Parts do
not apply in Section 9D. See General Regulations 1:2.