Re: carrying technique, if you are carrying a typewriter in your car, the best place to put it is in the passenger footwell.  If you have to brake suddenly, the machine is already in the lowest part of the car and will not go anywhere.  We used to do this with customers machines in the trade whenever possible.  One of the worst ways of handling a typewriter that I have seen recently was when I went to collect an Imperial 50 that I had bought on e-bay.  When I got to the chap's house, he picked it up using the thinnest part of the top plate (just above the segment) as a handle !  When I told him to stop, he told me that it was OK because it was cast iron !  That's the same cast iron that is brittle under shock and bending loads of course.  Miraculously, it didn't break.  Some people !!!!

Okay, curiosity got the better of me, and, feeling strong today, I decided to weigh my heftiest typers just to see what they run.
1936 Royal KHM......  34 lbs
1937 Remington Noiseless Standard model 10....  37 lbs
1940 Underwood Noiseless Standard....  40 lbs
1955 IBM model B (standard)....  42 lbs

Given there were around five carriage sizes available, it would of course depend, but with a standard size carriage the breakdown is: 23.4 lbs (machine) + 12.0 lbs (carriage) = 35.4 lbs (total)

What year was your SG3 manufactured, Kat? The model went through a number of changes during its production history, and with each iteration there were fewer optional carriage sizes available. With early models there were six different carriages available, the later German-made version only offered five, and by the time they were made in Mexico you could only pick from four.

Here are the net weights for the Mexican SG3 models, and as you can see they really put them on a diet because these are much lighter than the German models:
33 cm/13 in. carriage model = 14.2 kg (31.3 lbs)
38 cm/15 in. carriage model = 15.0 kg (33.0 lbs)
46 cm/18 in. carriage model = 16.0 kg (35.3 lbs)
62 cm/24 in. carriage model = 18.7 kg (41.2 lbs)