A little crude looking but cheap and effective:
1. big (at least 3/4") fitting in each valve cover, with a baffle inside to mask splash
2. big hose goes away from the engine sideways
3. to a big horizontal cylinder on top of the inner fender (largest diameter that allows the hood to close)
4. if possible, cylinders should drain back to the covers when stopped, otherwise a drain and hose to empty it
5. huge volume is possible: 3" OD × .060" wall cylinder 24" long is over 300" for both
6. a backfire will blow the connecting hose off, so strength is useless in the cylinder itself - no moly, no carbon fiber, just mild exhaust tubing
7. not as effective as an extension to the pan because
a. limited by hose size
b. air blowing up from the pan fights oil drain from the heads