awk
pode fazer isso:
awk '/Part/{i[$2]=$1;next}$1 in i{print i[$1],$2}' file | sort -t= -k1
Part1=STS768976N-4BT345432-X00001-87675789AAAS 90000
Part2=STS876578N-2BT234522-X00002-23456789UJHG 70000
Part3=ST9876887N-1BT876577-X00003-65778978KJUH 80000