Drop by a muffler shop and scavenge up a foot or so of exhaust tubing that will be a snug fit into the hole in the crankcase. It's a pretty simple matter to fabricate a standpipe that looks almost identical to the factory part by using the upper section of the existing road draft tube and doing a little welding. If you run the vacuum line over the valve cover like the factory installation, remember it will need to be removed every time you adjust the valves. I prefer to route the line around one end or the other of the valve cover to the intake side of the engine.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!