my guess is mid to late 70's (smooth tolex, white logo with the silver/blue grill cloth-painted black in this case). IMO that era of 8x10 cabs sound great.
Unless the speakers have been replaced, pull a couple of them and check the date code. That'll give you a good time frame. BTW - the square to slant back occured somewhere in 1973. I know because I have one of each that are all original and the speakers are all 1973.