No real specific numbers for you, but listed below are some notes I've kept from an old Ranger boat forum. Might give you a starting point. Basic idea it not too loose, not too tight, and prevent excessive sag on the leeward shrouds.
The tips were from a boat rigger who owned a Ranger, so a few of his comments are a bit slanted, but I'm sure you'll get the drift. Anyway, see the below stuff for some basic info.
When we riggers tune a rig, we put on our wizard hats and try to convince
the boatowner that it's voodoo magic that only we "experts" can achieve. The
fact is, any reasonably intelligent primate can tune a rig, and it's very
simple. This secret is only to be shared with Ranger owners, and should not
be shared with owners of lesser boats, as we still have to make a living off
all those Catalina and Beneteau owners.
1) First loosen the rig and use a main halyard or topping lift to measure
from the masthead to each side of the boat. The purpose is to center the
masthead directly over the centerline, using the upper shrouds.
2) Once centered, tighten the upper shrouds equally, making sure the
masthead stays centered.
3) Next tighten the lowers. If the boat has two sets, tighten the forward
lowers first, keeping tension equal. Attach the main halyard to the boom
tack fitting and tension the halyard. You can sight up the taut halyard to
see if the middle of the mast is bowing to the left or right of center.
Remember, the head of the mast is centered, if the mast is bowing, loosen
the lower on the "bulge" side and tighten the lower on the other side.
4) The mast should be straight athwartships and uppers and lowers tight. If
you have double lowers, the forward lowers should be tighter than the aft
lowers. If you have single lowers and a babystay, the babystay should be
tighter than the lowers. More on babystays later. The point here is that the
mid-section of the mast can be permitted to bow forward slightly, but NEVER
aft. When this is static tuned into the rig we call it "pre-bend." If your
main halyard is still attached to the tack fitting, you can use it to guage
how much pre-bend you are putting in the mast. On the masthead rigs that
most Rangers have, it should not be too much. Fractional rigs usually have
more, and can add a lot of additional bend with backstay tension.
5) Now tension the forestay and backstay. On some Rangers, such as the 28,
there is no forestay turnbuckle, just a pair of link plates with a choice of
pin positions. All the adjustment is in the backstay. The forestay can be
allowed to sag as much as 18" in light air, or set bar-tight with lots of
backstay tension for a heavy blow. Remember that on a masthead rig, the
backstay adjuster does not bend the mast very much. Its primary function is
to adjust forestay sag to power up or de-power the headsail. Put moderate
tension on the forestay if you have a good backstay adjuster.
6) The Great Rake Controversy: Very simple: Raking the mast aft increases
weather helm, raking it forward reduces it or even induces lee helm.
Excessive weather helm is bad, but lee helm is worse. A moderately straight
mast with a slight rake is right for most masthead Rangers, and you want a
slight bit of weather helm. If excess weather helm is tempting you to rake
your mast forward, then take a look at your sails, they're probably old and
baggy, and a re-cut to flatten them, or a new sail, is what you need to
correct the helm. If you feel the need to lean your mast forward, something
else is wrong.
7) Babystays: Some Rangers have adjustable babystays, often on tracks like a
traveller. Tune the rig at the dock pretty straight, but keep the tension on
the lowers minimal to allow the babystay to induce bend. Tension on the
lowers sets the limit on the bend that the babystay can create.
8) Multiple Spreaders: Applies to very few Rangers, but creates an extra
upper, or "intermediate" shroud. Simply start at the top and work down:
Uppers, intermediates, then lowers, keeping the masthead centered and the
mast straight from side to side.
TUNING UNDER SAIL
Sail upwind in moderate breeze and see if the leeward shrouds sag. They
should only sag a little. Tighten the leeward shrouds HALFWAY while counting
the turns. Now tack, and tighten the other side an equal number of turns.
When satisfied that all is equal, the mast has no sidebend, and the masthead
is still on centerline at rest, then pin and tape the rig.
This is a lot of information, but static tune should take less than an hour
if all the parts are in working order. Make sure no turnbuckles are bent and
that they can articulate in all planes (toggle). Also inspect all the wires
at the point where fittings are swaged, as this is the area where failures
occur. Notice that no rigging guage is needed to tune a rig.
Remember that wire rope stretches, and on many old boats stays can stretch
to the point they cannot be tightened enough. That's when you need to
replace standing rigging, as a loose rig is dangerous. A "floppy" rig in a
blow allows shock loading that can cause other parts to fail and bring down
a rig. The biggest mistake we commonly see on boats we tune is rigs that are
way too loose. If tightening your rig loosens chainplates that were bolted
to rotten wood, you needed to fix that anyway! Best to fix it before it
makes your mast come down.
Tune up, sail well, and keep those old Rangers outpointing everyone!