I've used and will continue to use Valvoline 20W50 non-synthetic oil in my TR4 motor (currently slated for a rebuild after about 120,000 miles) and plan to use Valvoline 20W50 Racing (non-synthetic, non-detergent) in the car's gearbox with overdrive. In the non-OD gearbox and rear end, I use 90W or 85W90 GL4 gear oil, non-synthetic. (Also avoid GL5 gear oil in the gearbox and diff.)
Overall, I've not had good luck with synthetic oils. I've heard they should be avoided in TR gearboxes, especially.
And, I believe you should neverm ever use a synthetic oil in a newly rebuilt engine, at least until well after it's broken in.
Every "modern" car I've used straight synthetic oil in has developed noisy lifters. This occured with both a VW Jetta and a Land Rover. The Jetta also definitely started leaking more oil, never leaked a drop before the change. I couldn't say if the Land Rover leaked more, hard to tell with all its typical power steering fluid leakage! Neither car had particularly high mileage.
I do use semi-synthetic Valvoline in my current Land Rover, but lifter noise definitely increased after I started doing so. Occasionally it clatters briefly when oil is fresh, this lessens and disappears after the oil has been in the car for a while. The car has only about 50,000 miles on it, certainly shouldn't have lifter noises! Previous owner used pure synthetic (16,000 miles) according to some paperwork that was in the glove box.
On the positive side, when I've tried synthetic oils or even semi-synthetic, there has always been a moderate to quite noticible increase in gas mileage.
Alan