Engine rebuild or engine change? big dilemma....

[ncp13]

I hate to be a bugger but a missfiring cylinder could be from a bad injector , bad ignition coil, spark plug , burned valve , and low compression on the specific cylinder etc...

Did he swap ignition coil with another cylinder?

P0301 is missfire on cyl #1 p0302 cyl #2 .... Etc and p0300 random misfire..

Check the health of your engine with a leak down or compression test. That will help you with diagnosis of your symptom too

Otherwise find a used 1nz engine and grab it :) its your cheaper option