I would agree on the sensibilty of using rod on this type of boat. The benefits would not likely out way the expense. Rod is expensive and unless you can get it x-rayed is hard to properly inspect. As for specs any competent rigger should be able to look at the terminals on the spar and tell you what size (diameter) rigging should be there. The clevis pin size is the first clue. Have you looked on this site in the specs archives? If I had to guess I would say 5/16 for the fore and backstay, 1/4" for lowers fore and aft, and uppers, and 7/32 for intermediates if your rig has them. But again you should be able to look at the pin sizes at either the mast or boat end to determine. Cant believe they lost your rigging...
One thing I will say about some of the sailnet posts is that I dont think several of those folks know what they are talking about. One suggested that rod rigging failed from a cracked swage. Rod is not terminated with a swage. One reason its actually better than wire. Another suggested its hard to carry a replacement stay. Thats nonsense as all you need is
http://www.colligomarine.com/. Wire is far more prone to crevice corrosion, and I cant tell you how many bad swages I see on boats with brand new rigging. Wire is also heavier and not as strong as rod. All that being said wire is IMHO the most practical rigging for a 1970 E-35 MK2. Dont take my opinion as any gospel though I would refer you to
www.briontoss.com for a true authority on rigging questions. Message boards are good for opinions but I am very leery about taking any recreational boater's advice without thorough research.