You know, the newest 760 pump arm (all black) might look pretty good on a 1377 - it is not a square block - looks sort of like a 1389 pump arm. I just checked the Crosman web-site but I see no schematics for this newest model.
I do not know for sure if it would fit a 1377. Maybe someone knows???? - , or you could call Crosman and ask. You could get the matching black grips for the Crosman PCP pistol. Now we're talkin'.