Hiya Steve,

The '71 142E was indeed a "year only" motor, at least in the U.S. market. It's variously given as having 130 or 135 HP, depending on the source. Same setup as the '70-'71 1800E.

Rating methods were not changed in that time span. I believe the later B30s had lower compression than the earlier ones, just as the B20E was derated to the B20F for in '72. Or maybe there is more smog stuff on the later ones -- I'm not that familiar with the details.

B30s all used the C cam because it suits the RPM range the motor is designed to sustain. That long, long crank and cam are a lot more subject to flexing at high RPM than the B20 equivalents, so the whole motor is set up to make power at lower revs. Note that even though HP figures are similar, the B30 makes a lot more torque (which I'm sure you feel when driving it).

As for weight, a B20 is around 340 lbs., so figure about 45% more for a B30: 493 lbs., and increase of 153 lbs. right there. The M410 is also heavier than the M41. Then add the extra wheelbase/body length, bigger bumpers, more luxury stuff, etc. etc. that's not weighing down the 142...