two questions

what i thought was the coolant overflow reservoir i now think was the washer fluid holder, i think someone just put the overflow tube in it as the washer mechanism didnt work. the question is was there an overflow tank? can i buy one, where does it install where does the washer reservoir install?

radiator question 1968 firebird 400 HO what radiator should it have? how many rows? how do i know if I have the stock one? and if I replace it what should I use? thought about buying aluminum and painting it black?

I use my washer reservoir for rad overflow. Works great.

Factory didn't use one at that time.

There are many aftermarket choices. The one I always liked was the 74-76 Nova reservoir setup. Its kind of tucked out of the way and very stock looking

You can add reservoir, it wasnt stock on these cars...I added one just initially to see how much it puked io=out as mine was running hot when I got it....I put it next to the WS washer fuid container, actually put reservoir in its place welded WS was fuid bracket to reservoirs bracket.

Still looking for ideas on the radiator
thanks

I'm using my stock rad for my 400 HO. Where do I get info off the rad for you?

Most go with Aluminum radiators when replacing/upgrading. I have a 3 row Al rad for my 400/468. Works just fine.

My advice on the overflow tank is to get one that shows the fluid level without taking the lid off. Plastic ones are the best for that although another member recently posted a photograph of an aluminium one with a sight gauge on the side. One should still occasionally take the rad cap off and check the rad is actually pulling the fluid back into the radiator. The shiny steel ones may look nice but one has to take the lid off to see what's inside. Also get one large enough to do the job. Mine is full when hot but completely empty when cold. The radiator is always full, the tank holds exactly the volume the rad expels when it heats up. I have to take the top if the tank and the rad cap off to check the level. PITA. I'll attach a few photos of one too small.

As for the radiator be aware that if you get a hole from a stone, or whatever, in your aluminium radiator you may not be able to repair it. Get a hole in you brass radiator while on a road trip and the nearest garage can most likely solder it closed. Not so with an aluminium radiator.I had to replace mine for that very reason.