the compression is at 150 on all 8 cylinders? if so, thats all good.
next check, if thats what there leaning towards, is do a leak down test.
test all 8 cylinders, make sure the cylinder your testing is at top dead center on compression stroke (both valves closed), make an adapter much like a compression tester (that threads into the spark plug hole) but on the other end you need a airline fitting to hook up to a air tank or compressor.
plug the air line into the compressor and into the adapter thats threaded into the spark plug hole and listen for an air leak.
if you can hear it out the intake, you have a bad intake valve, out the tail pipe, its a bad exhaust valve. if no leak, no valve problem.
repeat in all 8 till you find the problem, if there is a problem, then yes, you need head work.
the compression test is stating your rings are all good so rule that out.
My thought is, if they wont give you the compression results, it might be bogus, check your fuel and ignition first.
a leaking injector or regulator will give you a miss.
check closely on your cap and rotor as well for any small cracks and carbon tracking.
are any of your spark plugs fouled worse then the others? if so, start test on that cylinder first.
3-lot