Overheating Big Block

[mprat]

Now after finishing my 67 Chevelle, I took it for a test drive and it seems to have a overheating problem. It is a stroked 454 crate motor. Has aluminum heads, bored .060 has 10.5 forged pistons... I have a three core aluminum radiator, two electric fans, running a single belt march system with reverse flow water pump. tried 195 and 180 thermostat and nothing changed. When I took it down the highway and would reach 190 hang there a short time then up to 200 to 205+ I would get it back to the garage and it would blow water in the overflow and eventually on the floor. I tried it just sitting and at 190 it would start to flow water into the overflow tank which seems odd to me. It has a 16lb cap and I have tried two. The outside temp was 85 on several test runs. But the other day we had a front come through and at 75 I drove it and it stayed at 190, which I thought it should have ran cooler. the fans are working fine, I do not know how to proceed in what could be the problem. I have never ran a reverse flow pump. But we have run out of things to check... any ideas???