The pre-built lithium packs all seem to have a weak spot in the BMS unit that limits current draw. From the link it says in the BMS section:
60 Amp continuous discharging, 120 Amp peak discharge
Your upgraded motor isn't going to do very well if you limit the current draw from the batts to 120 amps.
The other thing that is concerning is the condition that is listed... "Frame, BMS, Display Meter are brand new, and the batteries 65% capacity".
There's another thread in the lithium section to a place where you can buy the Leaf cells for $50 each. Here's the link to that thread:
http://www.buggiesgonewild.com/showthread.php?t=161633
and a link to the cells:
https://batteryhookup.com/collection...y-module-gen-1
They are untested G1 at $50 each... Pretty incredible price...