You have to check is your car using standard shorty or low center of gravity lcg packs.
I didn't have good luck buying used lipos, especially race packs. Me personally I would not pay 30 for a pair
My recommendation is hobby wing just stock combo if you are on a budget, or just stock esc and trinity slot machine 13.5 motor.
3.1 is an old esc, hobby wing still makes it but under quick run 120 bl name. I would suggest to stay away from it. It's just way too old and doesn't have a lot of...