I may come to need a pair of helical gears to change a shaft direction
90 degrees, with a reduction of about 4:1 to 5:1 .

Though they are a bit large, the cheapest sources of these is the gears
from car axles. The stress they will be placed under in my use will be
drastically less than what they'd get moving a car around.

What does the measurement of car R&P sets refer to exactly? I can't find
any place that says.

Second I have noticed that many axles are not bevel gears but hypoids. I
would need to know the shaft offset to make a proper housing, since axle
pumpkins are way heavier than I'd want. Is there anywhere online that
gives that info?

If there is any other source of perpendicular ring & pinions around
5"-6" diameter I'd like to hear about it.
.....ATV's are around the perfect size, but at $200+ a pair, they cost as
much as the much-stronger 7"+ car gears.
.....Golf carts all seem to use parallel drive methods (roller pinions
instead of bevel gear pinions).
.....custom gear places would want $500 to make a pair of hardened gears
that size.
.....I have looked at a lot of surplus miter gear boxes, but they're
usually straight-cut gears, or have a reduction ratio that is too high.