There are a few issues with re-hardening.
(1) If already reground and then ground again after re-hardening, they will be well undersized. That has to be made up by larger rollers or a smaller race i.d. in the conrod.
(2) Besides roasting the outside of the race and requiring re-grinding, it will also impact the surface finish of the i.d. where it is a light press fit on the crank pin. Not to mention what distortion will occur on the i.d. You cannot hone it true, as that would then make it slack on the crank pin.
(3) Compounds like Kasinite are intended to impart a superficial depth of case hardening of about 0.005-0.010". The case depth for surfaces supporting rolling elements ought to be at least 0.040" and better if over 0.060" deep. That is why the carburizing process take many hours in a furnace, to diffuse the carbon that deep into the sub-surface. Granted, there will be some case left from previously and you might be thinking one just needs to 'top up' the carbon content at the surface. But you still need to have a high carbon content below that to a certain minimum depth to support the case, gradually tapering off to the carbon content of the core. If you don't, the thin, hard surface layer will flake off the softer substrate. Particularly if the transition between the case and core is abrupt. Also known as Brinelling. To get the carbon that deep, needs a long soak in a carburizing environment.
It is simpler I think just to make a new race. An additional advantage is you can make it so the final diameter is oversized, in order to use standard diameter rollers since oversized rollers are getting so difficult to purchase cost effectively. If making both a new crank pin and conrod race, then that does not matter so much; you can stick with the original dimensions.
In this application, there is really no reason for the race to be made of carburizing steel. It could just as well be made from through-hardening steel like a ball bearing race is. Avoids the costly carburizing step. And no risk of Brinelling. Douglas probably used a carburizing steel as the cost for carburizing steel is less than for through-hardening steel. And they were running the carburizing furnaces every workday anyway.
-Doug