I actually just aquired one of these today and found this thread while doing research on the gun.
Originally the "carbine" version of the Rossi Model 37 was designated the Model 57. The gun I aquired today came as new in its original box (bearing the guns serial number) and is labled model 57. The original manual is for a model 37. Except for barrel length the M57 and M73 are identical.
I found this referance Argentine Pump-Action Rifles
but feel that it is not entireally correct.
The Model 57 Gallery Junior was introduced in 1970. Unlike other Gallery series rifles, the Model 57 was sold in the US by Harrington & Richardson (and called the Model 749 by H&R), and in the US primarily carried the H&R name. The Model 57 was sold primarily sold in the US, and sales elsewhere were quite limited. For that matter, sales in the US were never high. The Model 57 was basically a Model 37 with a short 16.5-inch barrel, and the tubular magazine ended level with the muzzle. The Model 57 is the only member of the Gallery series which is no longer manufactured, with production ending in 1972. However, an improved version, the Model 73 Gallery Junior II, was introduced in 1975 (but not distributed in the US by H&R). The Model 73 is still being manufactured.
I believe my gun is of 1968 vintage (based on markings on the box) and was imported by "The Garcia Corporation" not H&R.
Another interesting feature of my gun is the fore end/ hand grip; it is short and has no grooves. I know it is original as it matches the stock perfactly.
I also have two other Rossi .22 pumps but both are Interarms imports and marked SA62...