Rex, Thanks for the prompt answer. If yours has lasted 30 years, that is good enough for me. I'll skip the case hardening.
I can fix some of the parts. For example, the expansion links are gauge plate and were noticeably hard. I heated up to bright red and cooled as slowly as possible before drilling the various holes in them. They are both now harder than the other mild steel parts but I suspect less brittle than they were. I will leave them in that condition and use gunmetal or bronze for the die blocks rather then the suggested mild steel.
Hmm – not that far from a running chassis excluding the pumps.
Phil H