What is the best Ford replacement 4 or 6 cylinder engine for a 03 Focus ZX3?

I purchased a used 03 ZX3 from a dealer last year and the engine has developed a knocking noise. Dealer disavows any responsibility and my mechanic says junk the car before the engine fails. The car has a manual transmission. I have seen renovations on fordfanatics.com using a mustang engine. Any master ford mechanics out there?What is the best Ford replacement 4 or 6 cylinder engine for a 03 Focus ZX3?look for a ford focus SVT engine and transmission it should fit needing some modifications but overall it will probably fit decent.What is the best Ford replacement 4 or 6 cylinder engine for a 03 Focus ZX3?what,s it got in it now? because sometimes if it,s a 4 then a 6 won,t bolt up to the transmission.