You can get reprints of the factory assembly manuals for the 67 Mustang. There are separate books for electrical ( AM0018 } , body ( AM0016 ), chassis ( AM0020 ), Interior ( AM0017 ), Weld & Sealant (AM0019 ). These books are published by Jim Osborn Reproductions Inc. and are available from most Mustang resto dealers for around 20 bucks.
The vacuum routing is very minimal on a 67 and is shown in the electrical manual but doesn't go into any specific details. ( just shows the lines in the illustrations). The chassis manual does show specifics on the vacuum routing for the automatic transmission modulator valve. I can't think of much vacuum line use on a 67 ( I have a 67 ).
There is the timing advance, power brakes, trans
modulator valve, PCV valve and that's about it. I'm about sure these manuals will give you the info you need. I don't know how many thousands of times I've referred to mine. I've about worn them out. Yes, they do cover the six cylinder cars. Of course the reprint of the factory service manual is available for the 67 also. This book I have also and is about 50 bucks. There is also a CD version for about the same money.
Hope this helps you out. All the best, ---Chuck