Woody,

You won't get any jake action in neutral by raising the RPM's, the transmission has to be in lock-up before any jake function. If you don't follow Jon's suggestion, just drive the bus locked in first gear and run up to 2100 rpm and then let off the throttle. You will hear and feel the jake if it's working.
While driving, you will get a very slight movement in the boost gauge when the jake is working.

Remember, the jake on the 8V is very whimpy compared to the 60 and you need high rpm's to get any benefit. On the low setting, it's just about worthless.