Is this old Locking Ring necessary for new BB
 

Should I put the old Locking Ring of old BB to the left of new BB please? The first two pictures shows old BB, the last photo is new BB installed on the bike.

for the new BB with complete round face at the right end, how can I mount a holder for chain guard please?

Your new BB is designed to use without the lockring.

+1... that internal splined piece does not require a jam ring nut. they use force exerted on the piece by a tiny bit of taper in the piece's bore to stay put.

and applying some grease to the frame, threads, and bore, is highly recommended.

ride it.

Thanks!