8 3/4 Sure Grip ratio change

4.86s are the right ratio for a streeter not like yours, assuming a cam of 230* or less. The engine will power peak at about 5200/5400 maybe a bit more. The shift rpm will thus be 5800 or a bit more. Assuming 5% slip in the TC, 4.86s will get you about 63 mph topped out, for a 2-gear run for fun.The starter gear will be 4.86x2.45=11.91, which will be all but useless. So.....For a 318 or a 273' sure, 4.86s are the ones.
But for you;
For a one gear run;
to 51mph,3.55s are the ones.
To 56mph,3.23s are the ones,
to 62, 2.94s are the ones.
If you have to shift, The Rs will drop to 1.45/2.45 =59%, or to 3400. Does your engine have power there? Probably, but not nearly as much as at peak.
If your 417 cannot smoke 3.23s to 56mph, on the street with street tires, then there is a problem.Find it and fix it. Also with a 417, and good heads, you can stretch them out a bit; There is no reason you can't hit 60 at 6200 with those 3.23s.Or 65 at 6500.All with the right gear.
Before swapping gears, I would spend a few hours tuning what you got. IMO a 417 with 3.23s could be an awesome street combo. The engine has enough torque to annihilate any street tires,with a reasonably low-stall, yet cruise at about 65=2600. Puuuuuurfect.