I seem to recall 38 rockwell for the SBC " pink " rods , so that does seem soft.
Rather than heating , I'd look at a Cryro treatment.
Much less distortion of the part and more consistent grain structure afterwards.
I think because the temperature control is tighter with freezing as opposed to heat.
Tooling rockwell numbers depend on material and end use , with forming tools typically using lower numbers and different types of steel than stamping or cutting tooling.
Powdered metals skew the curve a bit too , but their prices kept us from using a lot if it when I was in that line of work.
But crankshafts are not through hardened like most tools......generally a case hardening that is usually less than .030 deep......often much less.