Fuel tank venting??

That valve is designed to allow vapors to escape except in the event of a roll over, then a ball inside it is supposed to close it; however I suspect fuel would probably be coming out your filler should this event occur.

I have done a number of EFI conversions and in fact am doing one now for a friend. I never use those roll over vents, they just do not seem to be useful at least in a Mopar. On my Challenger I have a line that runs from the top of the filler neck (inside the trunk) down through the trunk dumping underneath the car. On my Cuda I have a similar arrangement except that the line runs from the top of the filler neck inside the trunk to the passenger side and then exits through the trunk floor via a bulk head connector.

The bottom line is that your tank needs to be vented with EFI, there are a number of ways to do this to include the stock system, EVAC system, etc. You can even use a vented filler cap and on your Scamp, thats probably what I would do. The down side to the vented caps is fuel vapors are always present and many people do not want this (does pose a potential hazard and your paint doesn't like it). You could take a page from the factory and run a long line underneath the car from side to side ending with that valve if you are intent on using it, but if the line stays under the car and you fill the car (as you normally would), you are probably going to get some gas dripping out because you will have fuel up the filler tube which will push fuel out that vent line.

In some cases, Mopar ran their vent lines all the way to the engine compartment and then up, in others they ran them up inside the passenger side wheel well to get the height and distance they needed to keep fuel from coming out of them. If you run a line up to the cross member on one side (the one the shocks bolt to) and then back to the other side you should be ok but you won't know until you fill it up. Technically, you could run the line up into the trunk and then back down under the car and that would suffice.