Your answer.
The '77 was factory rated @170hp but that is gross hp(with no acceseries hooked up) not net like they use today. It has pretty much the same motor as thre '79and '80 280ZXs and they put out 135hp(net ratting). So, you car(if its stock) puts out 135hp @the fywheel.
For performance parts check out victoria british(cant remember thier website) or MSA(zcarparts.com) Also you might wanna check you local nissan dealership, I think you can still order some parts from them but they are kinda expensive.
Justin T
'80 280ZX
'77 280ZT(comming soon, hopefully)