<<<You said it. Most engines cruise at HALF the RPM that
the bus engines do. That includes all the DOHC Honda
and Nissan engines that rev happily to 7K. The thought
of any pushrod engine cruising at 4000+ RPM is
frightening, especially when the redline is 5K.

Basically, the WBX and Type IV spin roughly twice as
fast as most cars' engines. Therefore, for every 100K
miles your bus has, the engine has 200K worth of wear
and tear on it. With that in mind, the maintenance and
repairs that the WBX and Type IV reqire make perfect
sense, and in fact the WBX comes off looking like a
tank. With the diesel tranny's gearing, just imagine
what the diesel has to do.

This is why I really don't try to haul ass in a Bus.
It's just not worth it. You don't feel much speed in
one when you do get rolling, anyway. Just have fun and
enjoy your Bus time. :)>>>

That is why, along with the engine modifications, I changed the gear-box to a SA .457 five speed, to drop engine RPM. 55 MPH is around 2800 RPM in fifth.  I rarely have to shift from fifth, at 55 MPH, unless traffic speed drops below 35 MPG, I hit a really steep hill or I need to accelerate quickly.
Fourth is good from @25 to @65 MPH.

Latest check on mileage, I was getting about 21 MPG with mostly city driving.

I could have used a .77 fifth gear, rather than the stock .85 but did not want to wait an additional month.  But as it turns out, the Engine's wide power band and new SA five speed gear-box are just about perfect together.

 I am able to be in taller gears at lower speeds, do not have to down-shift as much and able to maintain speed on hills in fifth with the increased engine power at both the lower and higher RPMs.

If the ground is level I test the engine by taking fifth down to 1500 RPM and then taking it back up.

I can cruise effortlessly at 80 MPH or 55 MPH...

Robert