@shon7,
You have to log atleast 10 Hrs (Actual including checkride time) on a multi engine aircraft which is recognised by DGCA (Which are BE-76,PA-34 & DA-42) in order to get a multi engine endorcement on your Indian licence.You donot need to fly for 20 Hrs (Plz refer to conversion flow chart available on DGCA website).However the Indian operators ask for about 25 Hrs of multi time (Actual + Sim).Also you might want to get a Multi IR(shoot minimum of 2 approaches in a multi to get an IR on multi as per DGCA & thts wat you'll be asked to do in your FAA multi checkride).Seminol is a better aircraft (and also cheaper) compared ro Seneca but sadly DGCA doesnt RECOGINSE the aircraft !!!
Regards
S.H