George Dammans book, "70 years of Chrysler" says the model 52 came out first with 2 wheel hydraulic brakes and they then fitted 4 wheel hydraulic brakes after March 1928. Over the years a lot of people have disputed this, and some have told me their model 58 and 50 cars have 4 wheel hydraulics. Perhaps these cars were upgraded, or did Chrysler offer hydraulic brakes as an option on cars?
I had 2 1928 model 52 tourers, one had 2 wheel mechanical brakes, the other had 4 wheel hydraulic brakes. I also restored a 1927 model 50 which had 2 wheel mechanical brakes.
Of interest, my model 52 that had 4 wheel brakes, had a factory stenciled date sprayed onto the inside of the frame, just forwards of the battery bracket, showing the frame was made in Dec 1927 and the engine main bearing shells for the same car, were date stamped April 1928.
I have looked back at some of my files, both the Model 52 cars I had were fitted with 12 inch diameter brake drums, and the drums on my Model G70 are 14 inches in diameter. The 4 cylinder cars brake cylinders are also much smaller than my G70.
"70 years of Chrysler" , says both the model 52 and model 62 were the same, 109 inches long, however that does not mean the frames were the same. A write up in WPC news June 1984, also says the 52 and 62 models were the same length, but they also mention that the 62 frame may have been slightly stronger, especially for the commercial vehicles. I actually wonder if this frame is a model 52 or 62 commercial, that would possibly explain why the spare wheel mounting brackets ( which are normally riveted) are missing off the rear x member.
Getting to the keyhole slots at the rear x member, if you look carefully at the picture posted by Kaiser. There are 2 slots just each side of the spare wheel carrier, these are NOT the ones for the tank straps and I have no idea what they were used for, unless they were used to bolt on rear bumpers or a trunk rack??. There are 2 more slots further out from the spare wheel carrier, these are for the tank straps.
One of the most defining ways of telling if this frame is a 4 cyl model 52 or 6 cyl model 62 is the flange on the differential. The 4 cylinder cars have a fabric flexible disc that bolts to a 3 "fingered" flange. The 6 cyl cars have a ball and socket universal joint and the diff flange is a more conventional round one. Perhaps Lyle can check this feature out.