1975 wetfalia overheating

[Vwking0803]

About a year ago I started off on my westfalia. It was running with unbelievable power. Constantly speeding up to 85 without really trying. After driving 75 miles I started to hear a slight engine noise but it was very quiet. I pulled over after 110 miles to fill up and could not restart the van. Turned over but no start. Towed home, 0 compression on three cylinders. Adjusted incredibly tight valves, between 10-60 psi on three aforementioned cylinders. Would start if careful with starting fluid and run but maxed out at 40-45 mph. I took the engine out, disassembled to shortblock. The three low compression cylinders had gouged pistons and cylinders, seized engine rings. I replaced pistons and cylinders along with exhaust valves. I thought the engine Engine ran good on 35 mile trips. Then my save my bug dipstick arrived. After installation I have found that I can drive 10-15 miles before the light comes on. I have checked the temp on the ending switch twice seems accurate. I am not running a thermostat, but hadn’t for 15+ years without a problem. I replaced the heads about 7 years ago with no problems. I replaced the exhaust with a 4 to 1 header and single quiet pack 7 years ago. I did replace the engine seal when the engine went back in. All tin is present, flap orientation has been checked, we blew air through the louvers at the back- no restriction, fan belt is tight, ignition timing verified, unplugged the vacuum advance, replaced the cylinder head temp sensor, tried a different air flow meter, oil is full, valves have been adjusted twice. Can anybody suggest anything to check? Thoughts or ideas? I am absolutely out of ideas.

[GARRICK.CLARK1]

Unplugged the vac advance. Have you used a strobe to verify the timing is good. Have you rolling roaded this engine . Is the fueling good