Thanks so much for the very informative replies to my question. I was considering going to 10W40 Castrol for the winter months, but I was a little concerned that it might be a little too light weight for this engine on those winter days when the temperature gets back up into the 60's here in South Carolina.
Before sending this post, I did go through the owners manual from cover to cover looking for ANY information on suggested oil weights. The manual looks complete, but there must be some information that wasn't with the car manuals when I bought it. I've been changing my own oil in all of my cars for the past 35 years. (That's about the extent of my mechanical ability, but it does make me feel like I'm able to do the most important PM service for the car).
I don't know why, but I'm still a little reluctant to go with a Synthetic oil in an older car that wasn't weaned on it. I'm probably wrong in being concerned.
Thanks again all,