cooling problems

i rebuild my 350 and threw it in my 68 chevy van, it runs really good, i installed a brand new 3 fire aluminum radiator with an electric fan and shroud, but I'm over heating just driving it around for 15 min, i don't have a thermostat and i redid my times. could it be my valves?

Not having a thermostat is often worse. The water moves through the system too fast and doesn't have time to cool down in the radiator.

The real radiator needs a surge tank with a recirc hose on it to let the air bleed out of the cooling system,,,,,did you get all the air out of the system with that radiator?

Yeah , air in the system is your enemy. If you have eliminated the  tank? you still need the high point in line fill and a coolant recovery tank along with a stat.

Ditto on the stat, the water/coolant, 50/50, needs to stay in the radiator long enough to cool, full flow will run hot. I just put in a recored radiator and a new 180 stat with my 6 cyl. You can watch the temp on the gauge go up and down between 165 and 180 as the stat opens and closes.

Alright I'm going to put a thermostat in and see how that works. I modified the new radiator and welded and aluminum bung on it to accommodate the stock fill can. But i feel like it still needs an overflow.?..?

Alright I'm going to put a thermostat in and see how that works. I modified the new radiator and welded and aluminum bung on it to accommodate the stock fill can. But i feel like it still needs an overflow.?..?

The surge tank also has a hose that goes to the coupling on the upper hose,,,,,,

remember-when these vans were NEW!! They never had  overflow cans , thermostatic Clutch  fans, electric fans!! They cooled fine then. Therefore- air flow & not circulation is the leading problem! With a =NEW Radiator!Thermostst =YES A=180F! after 1965 some mfg's added the clutch fans -usually GM. Do you have a shroud??

Clutch Fans & Shrouds= were the solution to factory air conditioning

I live in one of the hottest places in the US......I routinely eliminate thermostats and have never had any of my vehicles ever run hotter without a stat......My 91 Olds wagon now runs at 160 degrees with no loss of fuel mileage or drivability....... Times I've had overheating issues, it has ALWAYS been a malfunctioning thermostat...... I've been told that 1 in 3 malfunction right out of the box and I have found it to be more like 2 in 3........I WILL NEVER INSTALL A THERMOSTAT WITHOUT DROPPING IT INTO A CUP OF APPROPRIATELY HEATED WATER FIRST to see if it opens....I once replaced water pump, radiator, and hoses on a car, and installed a mechanical gauge because I didnt suspect the new thermostat.
I get that you are overheating without a stat, and I agree with the advice about a fan shroud and eliminating air pocket up top. I also would look closely at the lower hose for an aneurism, kinking or sucking shut. Also want to make sure that fan is running constantly until the van runs cooler than spec.......You didn't say what kind of rebuild you did, but if you did a high compression "hotrod" rebuild on a 350, it may just be too hot for a classic van........Air flow and radiator size are limited...