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Losing the torque converter is plenty offset by the heavy flywheel the clutch requires.
Multiplying first gear in the trans times the axle ratio is your launch ratio. For the V8 Mustangs and V8 Camaros, from the sixties through 2000+, the majority of drivers of such cars feel a launch ratio of 9:1-10:1 is the sweet range for a manual, but with an automatic, more like 10:1-11:1, which seems contrary to the idea of having the torque converter. But a stock GM V8 torque converter multiplies the torque by roughly 1.6:1 when the car isn't moving. Your Ford is likely between 1.4:1-1.8:1, unless you buy a race converter. Those can approach 2.5:1. Even so, once you begin moving, the multiplication drops to effectively nothing.
Most stock V8 GM converters slip roughly 400 RPM at WOT, so when the engine is spinning 5800, the trans input shaft is spinning 5400. So there's still a little multiplication, but on the chassis dyno it shows up as lost efficiency, mostly from having to pump the ATF at pressure, manuals don't have that problem.
ICEs convert heat to rotation, torque converters and ATF pumps do the exact opposite. Lost efficiency.
With a manual, you want to gear it for at least 600 RPM in first gear at 5 MPH. Any less RPM at 5 MPH will feel wrong in normal driving. 9:1 gearing gets you close with tires around 26" diameter. Typical for ponycars, your tires should be taller, so you'll need slightly more gear.
A Ford 4.6L V8 is perfectly capable of 1600 RPM at 65 MPH, any less RPM than that is your own experiments, not Ford production offerings.
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