Help for ditloids needed please

[Trussell]

I have struggled over a few weeks now with these last few and would really appreciate some help with them.
a) 1.68 = D of a GB (I)
b) 2 = W in SS in the B
c) 16 = PC in a RD of C
d) 56.5 = SG of BRL (I)
e) 180 = IDL (DL)
f) 1750 = JCF
g) 1852 = MOI the L
h) 1991 = LDIFM
Many thanks in anticipation

[bridgenut]

I think that d) is 56.5 = standard gauge of british rail lines ( inches)

[Dinkypuzzled]

a. diameter of a golf ball (inches)

[grasscarp]

e) 180 (degrees) International Date Line (Date Line)
c) 16 picture cards in a Royal deck of cards

[Trussell]

Thank you all so, so much! I had played about with picture/playing cards and discovered the word 'rouennais' and wondered if this meant the aces were included - so thank you grasscarp, for sorting that.
Thank you bridgenut - i was on the wrong tack, or should I say lines(?) of Specific Gravities, and thank you dinkypuzzled as i should never have thought of a golf ball.