(489) 3.23:1 to 3.55:1

My 67 Barracuda has a 489 case in it with 3.23:1 ratio running 26" tires. Also has 69 A833 A-Body 4 spd. It is some kind of locking diff I think, as when I backed it into my shop after getting it off the trailer from purchase the tires broke loose and left 2 even black marks on the concrete. It's uphill into my shop. Not sure if it's a Sure Grip or not. Diff is still in the car. I am thinking about trying to swap out the ring gear and pinion to a 3.55:1 ratio.

Would it be too much trouble to swap out the ring gear and pinion? If not, what would need to be done as far as setting it up? Would I need to just adjust/shim gear lash between the ring gear and pinion or is there a lot more involved even if I wasn't planning on completely stripping down the entire unit?

If it would just be adjusting the gear lash on the new gear and pinion does anyone have any recommendations as to brand(s) of gear set? I have glanced at Richmond but haven't dug too deep into the weeds yet. Gathering parts for the 340 engine (+0.030) rebuild right now. Shooting for ~ 400-425hp at flywheel. Thought it may need a stouter gear set for the hp? Not sure on the torque value yet. Some write ups I have seen online (Motor Trend) and such with similar build components as I have accumulated showed around 428 lb*ft of torque. I figure every engine will be a little different though.
Best I can tell from case casting number decoder(s) the tranny has a 2.66:1 first gear ratio, unless someone has possibly changed it out.

I know this is a long post but another thought was that if I kept the 3.23 as it is, would swapping the 2.66 first gear to a 3.09 be enough to make a friendlier low gear cruising experience. Don't want to have to keep clutching on a main street cruising night if I don't have to and not require over 3k rpm to run 70 mph on hwy.


Appreciate any thoughts/recommendations.