Code 43 Knock Sensor

Just put brand new GM 5.7 long block in truck, new distributor, fuel pump, water pump and so on. I have about 120 miles on motor last 2 trips to work "service engine light" came on never had light come on before. Turned truck off went away drove 3 days later same issue. I'm wanting to know why now? Is that sensor in front of starter on side of block or is there another style for this year 1989? Seems to ping a little under low speeds when you stab the throttle and has a very Slight stumble while idling. Timing is set 0 degree BTDC. Any quick checks or adjustments to get it performing at its best. It also seems to run a little rich. Thanks for speedy response your advice is kindly appreciated. Frank