I duno if you'd want to rethread bolts anyway. Cutting a thread cuts through the grain stucture on the steel. I'm fairly sure that the likes of ARP make their threads by rolling rather than die cutting.

I was hoping to try cheaper than ARP but it will be cheaper to
go ARP in the first place as Im sure shortening and re-threading
stockies will cost just as much and be weaker than ARP.
Thank you! It will stop headgasket issues prone on ca20 from factory.

It be worth writing down the length and thread diameter/pitch and then check with arp as they almost certainly would have some bolts or studs that would be the right sizes (and might be off some totally different engine).

Just wondering if anyone out there knows of a mob
that can shorten my head bolts for the ca18 hybrid
Im building.
I want to use the twin cam bolts on the sohc head
but they are too long. Also the ca20 head bolts
are supposedly the wrong length as they are made
for a deeper block and are thinner.
The ca18de bolts are 10mm and the sohc are 8mm.