PM 88Man and ask him as he has a real good handle on these things.
The number of 284's made is quite high. The 1963 intro of the 284 caliber makes it the most desirable (pre-64)and I paid $600 for mine even though it is only the checkering that is different. Realistically $400 to $500 for a post 64 version. For some reason, the 1963 model 88 in 284 draws a good premium.
Take the clip out and look for a "C" stamped on the top between the holes for the base. If there is stamp, the firing pin has been changed by the factory authorized depot.
Best bet is to keep it and shoot it! They are a wonderful gun and a great caliber.