read last 5-6 page. i send my confing couple of times. i not use overdrive .

"gpu_conf" :
[
{ "id" : 0, "intensity" :56, "worksize" : 8, "threads" : 2, "target_temperature" : 59},
{ "id" : 1, "intensity" : 56, "worksize" : 8, "threads" : 2, "target_temperature" : 58},
{ "id" : 2, "intensity" : 56, "worksize" : 8, "threads" : 2, "target_temperature" : 56},

gpu 900-910mv
mem 900-905mv

your gpu is too low. i have vega56 with 64 biso and my gpu  go on 1450mhz.

intesity for vega 64 : try 56-58-60