8 3/4 gearing - 3.23 or 3.55?

That kindof depends on the not-so-mild cam ....... and your elevation.
There is no point in trying to cruise a big cam at low rpm, in terms of fuel economy.
At or near sealevel; I'd gear a city car to hit 60mph in Second gear(A904) at about 200/300rpm after the power peak. With a 5000 peak, I'd be thinking 4.10s; for 60mph=4430 @zero-slip/say 5100 on the tach@15% slip.
But I wouldn't be taking it far on the Freeway on account of 65=3310 by the math/ say 3480 on the tach@5% slip.....

Between the two offered gears, I guess 3.23s. Why? because 50mph= around 5600 on the tach at the top of first gear, whereas 3.55s will be hitting 6150. If it's slow off the line, that's what they make hi-stalls for. If it spins 3.23s thru first, it won't be any quicker on the street with 3.55s.

But as the elevation goes up, and the engine loses power, sooner or later I'd be wanting the 3.55s.