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So yes when you speak to the classic car buffs that tear engines down to the core and rebuild them after cleaning every crevice you'll learn they typically go detergent all the way. But if your engine has never had detergent and you run detergent oil there is a good chance something will get loosened up and plugged somewhere creating all kinds of problems. Oddly enough you point to an obvious issue. Everything is gunky. That gunk can come loose even with non-detergent oil. I'd keep it as-is unless you're willing to do a teardown and clean it thoroughly IMHO.
The engine below was apparently swapped from non-detergent to detergent when detergent oils came out. It had never been opened before we took it out of service. There were no problems with oil pressure, clogging, or spun bearings with it in this condition. One cylinder lost compression so it was replaced. No amount of detergent on earth could break up this goo.
