not knowing the car or the cage construction or floor etc.
recommended;
shoulder harness should pull you 'back in the seat'
not 'down' so much, as just back 'holding you in place'
the downward pulling/compression if you roll
is really common to cause breakage/severe back problems
you really need a properly placed cross bar
just below your shoulders,
to attach the shoulder harnesses properly
so it doesn't create injuries
5 point harness
1) is a crotch strap
(that keeps you from sliding under the belts in a wreck/rollover)
2) shoulder straps
2) a waist strap/seatbelt/lap-belt
4 point harness
same basic design as above
but has no 'crotch strap' between you legs
some people like & some classes, require, suggest
some sanctioning bodies NHRA/IHRA tech,
require some sort of arm & head restraints too,
neck collar or Hans Device,
a fire jacket at a min at some min et/speed level (not sure what now)
or sfi certified 3 layer fire-suit
(if the trans isn't shielded or inside the car with you, no trans-tunnel etc.)
depending on how fast & sanctioning body rules
lots of variables to consider
a lot;
depends on the floor, understructure & mounting types
some are wrap around the roll-cage style,
some bolt to/thru the floor
with steel floors &/or reinforcement,
back up fender washers & steel plates,
threw bolts & mounting rings/eyelets
chassis reinforcements for belts
(when you have a cage it changes or can change requirements to the rules
of what specific sfi safety equipment, is needed drastically, do your due diligence)
really depends on the cag style, material in the floor & frame etc.
if it runs 11.49 et or slower a 6pt bar
(IIRC) with a 4pt harness
(only a quality locking lap-belt in most cases)
is within or exceeds the rules
9.99 et or quicker or 149mph & faster,
the rules are far more strict sfi certified every 2 years, sown on patch
far more safety equipment & a comp. license required
get a NHRA rules book or go to their site & rules
it shows belt placement
I hope some of that helps
good luck