Long-time Para owner here.
The P13.45 is Para's Commander-size double stack. The grip and magazine are a unique size -- the magazines and mainspring housings are different from the P14.45. P14 magazines will work, but they protrude from the bottom of the grip frame. Actual P13 magazines are somewhat difficult to find.
Is this pistol a Para-Ordnance, or ParaUSA? The Para-Ordnance pistols were made in Canada. When they moved the company to North Carolina, the name changed to ParaUSA. There was a period near the end of the Canadian production and the start-up in North Carolina when their quality control went down the sewer. Knowing the serial number might help to get an idea of the production date, but the serial number lookups you get from Remington now that they took over para are generally spotty. (And, now that Remington has been broken up and sold off, I don't know if they ever try to look up Para serial numbers.)
The good news is that the pistols are all still solid pistols. By now, any from the "iffy" production period have probably been tuned up to function reliably.
One thing to watch out for is the proprietary Para "Power Xtractor." It was an idea that looked good on paper, but didn't work out well in practice. You can tell if the gun has a Power XTractor by whether or not it has an 'X' in the serial number. Para pistols with the Power XTractor can't use a standard 1911 extractor unless you fit the extractor tunnel with an adapter sleeve. EGW Gun Works, in Pennsylvania, offers a heavy duty replacement for the Power XTractor. IMHO, it's a "must have" upgrade for any Para with the Power XTractor. I think the EGW extractor sells for around $60, so factor that into what you're willing to pay for the pistol.