How can you be sure that this is aircraft operating flight? I flew 9W on BOM-CMB-BOM once and both flights were operated by a wingletted 737 with 2 rows of regular domestic type J (38"-40" pitch).

AFAIK only 4 737's that were originally operating BOM-SIN-BOM non-stop route had the 4 rows with 58" pitch. The same aircraft also did afternoon BOM-GOI-BOM in the day. You should pray you dont get one of these 4 because these are in pretty bad shape interiors wise.