I love this "woulda, coulda, shoulda" about the Production car rules. In the
real world, it's not that important, but for those who research "a snapshot
in time", it is!
Productions and sedan rules are different.
Production rules are based on domestically formulated, wholly SCCA rules, be
it 1962, 1967, 1969 or 1973 (the commonly available reprints, available from
SCCA in Topeka, KS)
Sedan rules are based on FIA Group 1 and Group 2 rules from 1965 changing at
the end of the decade (the reason why FIA Historic in Europe often
advertises a 1965 cut-off date) modified by the SCCA to be more liberal for
the 2.5 Challenge.
In preparing a PL 510 (early Datsun sedan), threaded collars (without
retaining stock, unmodified spring perches) WERE permitted in Trans Am (r)
by 1972, see the book "How to Modify Datsun Competition Cars", HP Books.
Threaded, adjustable collars were NOT legal for SCCA Production class racing
until after 1972.
If CVAR wants to award bonus or penalty points for "period-correct"
modifications, that's their business, but in answer to the first of two
points raised by Jack Woerlhe, adjustable spring perches were NOT legal at
the time on Production based cars.
I prepared a disc-brake front, drum-braked rear, stock steel fendered, 2.4
liter 1971 240Z for SVRA competition in 1995-96. It DID have threaded
collars located at the bottom by the stock, unmodified spring perch, just
like JR remembers "fudging" at Sharp's during that time. I thought that was
a reasonable compromise.
Now, even some Turner 950's in VSCCA and Elva Couriers in SVRA have threaded
body coil-overs (at least in the back).
What should be versus what is then becomes the problem...
(happy to be racing at VIR for the next five days...)