I have another solution. I used this on my old Mustang, and it works great. I mounted the Moon Equip. 2 qt. spun alum coolant recovery tank to the driver's side inner fender with self-tapping steel stud screws and ran the hose back up to the surge tank.
This allows for the coolant overflow when hot to burp into this tank while the surge tank connected to the intake manifold is always full. I used a 4 lb cap on the Moon tank and a 12 lb on the surge tank. When it cools off, any voids are siphoned back up into the surge tank and the total system always is full. Beats spilling out onto the road or garage. $107 from Moon. And it kind of keeps with the period correct theme.
Doesn't really matter where you mount your recovery tank, as long as you never let air into the system, or else it won't siphon. Fittings should always be at the bottom, so not a good idea to mount horizontally, unless the fitting for your hose it at the lowest point. Good luck.