The metal shavings in the oil would worry me. Greatly.
I don't know how you can tear the motor down enough to sufficiently flush all of the complex network of oil passages clean, much less rebuild anything, for $4000.
For that $, I think I'd start with a known good 3.2L motor from an S and do the necessary upgrades to that while it's out of the car--cam chains/adjusters/ramps, AOS, water pump, IMS, RMS, etc. That would likely run ~$10k at a minimum...
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'02 Boxster S
'16 GTI PP
'17 Bolt (with a B)
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