What i done when my GU (not a GQ i know) 2.8 had issues
After finally spending way to much on the head cracked issue,over 4K on the top end alone
(Brand new bare head , labour,parts ect)
I sold it real quick while it was running
I was at the time in a bind re wheels,so it was fix it then unload , or sell it not goin for near nothin
If i had the choice now, and had the time,that i didnt have then
For 4K and time on my side,it would be as i mentioned a 2nd hand motor
Or look for a power upgrade
I just wouldnt spend 4K on a 2.8
Should be able to get a fairly good nick complete GQ 2.8 for around that money