I bought a compression
test kit that included several adapters including one that matched the injectors on the 4.236 from Amazon for less than $100.
I've never had anything made at a machine shop for less than that.
Biggest difficulty doing that test was removing the injectors.
They will inevitably be stuck in the head
If you can, take your time and let your corrosion
breaker of choice soak in for a few days before even attempting to pull them.