The logic for your dates works (I'd probably vote for the Memorial Day weekend one), but I'm still confused on a couple of points to make this whole "1958" thing work out:
1. The exterior of the church as seen through the doors at the end of KOTCS matches the weather in New Haven on October 18th 1957 (the canonical date by Lucasfilms) : 67 and sunny (Mutt is still wearing his leather jacket, the other guests are dressed appropriately for a mild October rather than late May, so it still seems as though we're trying too hard to make this work.
2. Are we eliminating Indy's daughter from YIJC? The YOUNGEST she can be in 1992 is 34. I've always imagined / hoped that what became KOTCS would have Marion and Indy end up married so that it was Indy and MARION'S daughter on the show. A 1958 wedding would make Indy's daughter 17 years old when she had her first child. And if Indy's daughter isn't from Marion, then she'd have to have been conceived with another woman between 1952 and 1957 and would have to be "discovered / revealed" AFTER Indy and Marion are married. Do they really need more relationship drama?
3. Where did Marion's middle name come from?