I highly recommend you to change your rods. I was struggling to get my bed level on my sd3, until i swaped the carriage for the lawsy, and changed my rods... Come to find out, my original rods were not straight !!! now I have no leveling problems any more.
Also, your original rods are imperial size. they are a little over 8mm in dimension, I don't remember the exact size in imperial, but they are bigger. And on top of that, the old rods are hard to extract from the old carriage without braking them.
Save you some hassle, and the rods are not very expensive, you definitely need to go for it.
I confirm as well that lm8UU are not all the same ! they are cheap linear bearing, and so, their tolerance are not consistent. so you should get some spare to be sure everything slides smooth.
Original belts and pulleys are just fine
Good luck with your mod, you're gonna love it !!!
SD3, early 2013. Silicon 200W 8x8 heater bed, lawsy carriage on 8 mm hardened chrome shafts, E3D V6 and lawsy MK5 extruder, ATX 350 W PSU, Custom build plywood enclosure, azteeg x5 mini smothie firmware, with vikki 2 screen, fishing line conversion and pulley conversion, M5 Z rod. Calling it Gran'ma, going strong ! <3