Like stated before 3k swap < 6k swap
1JZ - As for your concern about the motor and its info, It will come with time/experience and if all goes bad you will still have your mechanic buddy to help you troubleshoot/source out your problems.
+ 1JZ bouncing off the rev limiter/screaming = sex to the ears.
Seems like the obvious answer - you were looking for assurance I'm guessing.
