engine is getting hot

I rebuilt this engine during the winter and finaly get it to run today, I drove it for I would say 10 min, and notice that the temperature needle was around the "R" of normal, and I would say that it's worrying me a bit..

The A/F gauge was showing a stoich/rich condition

So except a lean condition, was could 'cause a kind of "overheating" like this?

Bad timing?

air in the cooant system did you try burping the system..
R in the normal isn't all that hot but I don't trust the factory gauges.

I feel a but stupid to ask that, but how can I burp the system?

some have a bleeder valve on the highest point on the system that you open and let the air out. But they don't have that on the Fox bodies so you could park up hill and get the rad cap higher than the rest of the system and let it run with the rad cap off an add coolant when if it starts to get low. Squeezing the upper rad hose sometimes helps speed up the process.

Another method is drilling a small 1/16” hole in edge the thermostat.

I would cool it down, remove the radiator cap, and let it run until it warms up. When the tstat opens, it should let some air out, and then you can add more coolant. It may take a couple of tries.

Also make sure the fan is running....