Rossi does not address the use of +P ammo in any literature I can find. If the revolver doesn't say +P on the barrel, I'm going to say NO, you shouldn't try to use it.
Mandatory Warning: .38Spl +P+ ammo should not be fired in any .38 Special revolver, other than possibly an N frame S&W .38/44. Some of this ammo is loaded close to .357Mag pressure levels and is intended only for .357Mag revolvers. That said, most +P+ loads were taken off the market decades ago; AFAIK there is only one +P+ load available today and it is supposed to be sold for law enforcement use only. However, I like to repeat this warning in case you shop at a mom 'n pop gun store which may have 20-year-old merchandise on the shelves.
Regarding comparisons of this gun to modern Rossis and Tauruses (Tauri?), I'm not an expert on Rossi, but it's my understanding that older models like the M68 were virtual carbon copies of S&W models, and were built on S&W tooling that had been sold to Rossi along with a license to produce the guns. However, these older Rossis have a reputation for being inferior in quality to genuine Smiths, particularly in fit-and-finish.
Rossi has since been bought out by Taurus and revamped their product line. Their newer products are more accurately described as "inspired by S&W" or "S&W pattern" rather than direct copies. IOW I can't tell you exactly what's different between an old Rossi and a new one, but I can tell you that they are substantially different in many respects.