back to the OP-
this sounds like a question of 'how cheap can I go,.,.' ?
if you stack (2) .030 with used 3.3s =
will the setup be close enough to not manifest any problems?
no-one can answer that, besides either -
probably, probably not, or maybe. pick one.
as Pope said, what *should* be done is -
Your machinist sets up your head.
this *should* (if your machinist is competent) include
measuring installed (closed) and open pressure for EACH spring,
measuring 'closed height' after the valve grinding,
and calculating 'open height' with the specs for the cam you plan to use;
there is usually some variability,
typically not meeting a desired closed pressure,., ie one or more springs is 'soft',.
if deviation consider too much, then shims are used to bring the closed pressure up of soft spring(s)..
WHILE making sure that coil bind at max cam lift doesnt occur,
or a max open pressure isnt exceeded.
this is part of your 'valve job' or 'assembly' charge.
nothing wrong with using shims, in fact *not using* them means -
not much detail went into equalizing the springs..
IF you do not have this done when installing :
used, old OE,
new OE or OE replacement,
used or new 'hi-performance'/aftermarket,
new or used non-OE part like conical springs or toyota valves,
THEN you are ignoring a critical aspect of your 'rebuilt head',
at least take yur springs in to the shop and have em checked;
might cost 10-20$ or some beer, or free ?
And again, back in the day, there was no mention of springs.
do you mean shims?
zero points for bringing up history.
if 'back in the day' "someone" set up a head with 3.3s and didnt check installed pressure ,
then "someone" made the mistake...
it *should* have been part of the install..
The 3.3 conicals are 60 psi closed, so to make them half decent, you need a ton of shims, waste of time,
where are you getting this 'fact'/generalization?
cuz its wrong,,
when my head was set up, my machinist found - as expected -
my used 3.3s were 10-15 lbs low on closed pressure (I asked for 105#);
he also found that adding .050s (or was it .050 total? I forget..) brought them all up within couple #s of 105..
problem solved, no need for "a ton" of shims,
no extra time invested - this is part of a routine valve job labor
either by the proper conicals or get HD stock type replacements.
or find someone competent to do your machine shop work,
that isnt baffled by the 3.3 springs..
wait lol you'll STILL need someone competent to install your "new" parts
install aftermarket 36.8mm exh valves on stock seats with multi angle cut - no problem, no extra charge
install dual spring teflon valve seals - no problem, no extra charge
install wacky v6 3.3 spring with GM retainer - no problem, no extra charge
install 'PT' lifters with Pope shims and verify proper geometry maintained - no problem, no extra charge
in fact this was all included in the 125$ "SOHC 8V 4-cylinder valve job" cost ..
altho that was 7 or so years ago;
it may be 150$ now ;)