[Bob Phillips]

Thanks again for all the comments and input. Dave and Lynn, I think the current rating for tensile strength in grade 8 bolts is 150KSI ( 150,000 pounds per square inch) vs 120 KSI for grade 5. Regardless of the actual value I am sure you would agree that modern high grade bolts would be preferable to the original and now stressed and aged bolts. I think that C4 ( and C1) owners should expect to replace these bolts at any point when they have their engine apart for overhaul or repair.
I have thought about trying to use the -46 improvements on the older style crank, indeed it may well be possible to simply use the rear of a -46 crank on the front of a C1 or C4. The issue I think may be one of correctly balancing miss matched parts, cranks, pistons etc. This is something outside my experience but as I have extra -46 cranks it may happen some day. Maybe this would be a good point of discussion for a future post.
Dan, thanks for your kind comments about this thread. There are not many places you will find informed discussion about 975s, and the goal is to keep as many of these fine old engines alive and running. You are also correct about my old C4- I take satisfaction in knowing it went to a good home.
Your comments about proactive measures to keep these engines alive and well ( high grade fuel, higher idling speeds etc) are right on. While radials are high maintenance powerplants there is nothing better than the sound of one starting up, with its coughing, belching and smoke. You gotta love it!
Best wishes to everyone for the Christmas season!