whats normal operating temp range for 77 g10


I got a 77 Chevy g10 van with the straight inline 6. Its a 3 speed manual with everything I think stock and original carburetor. its probably over 200,000 miles on it.I only had it a few years now.
I own a few older vehicles so I cannot remember if I replaced the thermostat or not in this van but a year ago I did a really good radiator flush with radiator cleaning product. Before the flush the heater was not too hot in the winter. After the flush the heater works fine. There is an aftermarket temp gauge previously installed in the van by previous owner. I notice a range of where the needle goes on this van, and it seems a bit hot sometimes.
So in summertime When cruising around on flat ground at say 30-40 mph without traffic lights or going down hill the temp gauge is usually at about 185-195. But it will creep higher if I drive with any stop and go with enthusiasm or trying to get to my destination fast.
When i do that in stop and go traffic the gauge is more like 200-205. 200 is also where it will be at if I just leave the truck idling warmed up in my driveway without moving. It will be at 200 a bit over 200 if it is a hot day outside. But what concerns me is the highway driving temps in the summertime.
At HWY speeds or anytime Im trying to accelerate to get to hwy speeds like pushing 70 and over or especially when going up hill or any incline I will see the gauge creep up some. It will get to 205 and 210. ( It almost gets halfway between the 200 and 225 marks). when coasting it will take a while to come back down and usually.Since its only a 3 speed manual so at hwy it is running its hottest its at high rpm.
When I shut off the truck the gauge will climb even higher sitting without the water pump going. sometimes up to 220 or 225. It cools a bit when I turn the car back on it will slowly go back down to 205
Does this seem normal or is it running a little hot? I see on websites normal operating temp for modern cars is 195-220 but this is a 77. should i throw in a 180 thermostat? or add after market electric fans? Since this truck is so old and a manual and carbonated I do not know what is normal.
The engine power is fine for its age. Im impressed with the stock straight 6. It has pretty good power and torque, especially from a stop at the get go. It maintains speed at 70 or 80 mph even can do pretty good up a hill on the hwy, although i usually do not push it. I even have towed a utility trailer with it no problem. It sometimes (very rarely) will have some dieseling after shutting it down. I will soon be checking the spark plugs which i never did since I bought the van.