relax do not panic please.
660 engine of any JDM , the rebuild is not possible. overhaul parts are not available.
engines from scrap yard are equally worn out as yours and only waste of monies.
visit a workshop which can scan your vehicle and conduct compressions test.
engine oil grade for every JDM class engine is "0W-20" only. any other engine oil grade can create serious performance issues., as you reported above.