No, it must be #8 if you are using #4 conductors.
Your entire first post alarms me. The fact you seem to be planning this work without knowing the individual conductors need to be in conduit is downright scary. Have you priced out 4-3 NMB wire, or 6-2NMB? Note that 6-2 NMB is NOT supposed to be carrying 48 amps continuously, but #6 conductors in conduit would be fine at 48 amps continuous, and then you could use a #10 ground wire.
THHN/THWN-2 Copper Wire | WireAndCableYourWay.com can supply #6 THHN at a considerably lower price than Lowes. Strangely their #4 price is higher.
Using flexible armored conduit may well be an option, but be aware the clamping requirements are different for conduit than the NMB clamps you have linked.
I assume you've selected the right MODEL/BRAND of breaker, to match your current panel.
That's INCH lbs on the torque. If you give it 50 foot lbs, the backplate will be utterly destroyed.
A cheap 1/4" torque wrench is only like $30. It also wouldn't be very hard to put a 4 lb weight on the end of a one foot bar strapped to a socket wrench, sticking out horizontally from the screwdriver bit. 50 inch pounds is VERY firm when done by hand with a screwdriver. Probably near the limit of many people's grip I'd wager.