I would also like to know opinions on these.
I've just been looking at the B3121, it's 21# and 1380 cranking amps, not as much power as my odyssey 1700 but 45# lighter.
Mick

69 Dart GTS 440 mopar .590 cam, Edelbrock heads, 3200#
best et 6.45, 106.78, 10.14, 132.88 mph, 1.47 60ft
best 60ft 1.36