I think that you have the terms hydraboost and hydrovac mixed up.
I have been running a GM hydraboost in my 64 for 19 years now works good. I did have a detroit diesel and you can't draw vacuum from them so this is the alternate solution. they were available from all Gm trucks(light duty) that ran diesels( whenevr they came out) from about 75 onwards.Mine was out of a 75 4 x 4 suburban
ron
