You can keep the original cap on the radiator . all you need to do is direct the overflow pipe into a container with the pipe reaching almost to the bottom. Then fill the can about a third of the way with coolant. Then instead of the rad belching out on the ground it will go into the can and can be sucked back into the rad as the system cools
The radiator cap has to allow pressure to escape from the rad. or else somthing will burst.
The ones with the pressure cap on the overflow tank have a "dummy" cap on the rad. It seals to the top lip but has no valve in it, so the overflow pipe and overflow tank become part of the pressurised system .
The plastic type "catch can" system I described first is much easier to set up and is just as effective.
Just make sure your can is vented. in other words, don't use one of the factory types with a pressure cap unless you put the dummy cap in the rad.
Hope this helps.