Thanks for the input you guys, the tranny input shaft idea that is.
Recalling from the hot rod days, the input shaft from a Muncie for
example enlarges from the spline to a bearing carrier diameter, may
even have a gear mounted to it. I will search for one and I'm sure I
can come up with some adaptation to a spline coupler ( found one at
surpluscenter.com ) for my pump if that becomes necessary. It has been
suggested from previous posts that because the pump varies its
displacement and therefore its output down to zero flow when there is
no load a direct coupling without the clutch disc might be the simpler
and beefier way to go. It doesn't seem too difficult conceptually to
weld a spline coupler onto a plate that bolts onto the flywheel using
the pilot bearing at the rear of the crank as alignment reference. The
trueness of this adapter/coupler would be guaranteed through lathe
work, of course. Yes, I was intending on using the bellhousing to
mount the pump onto. As you say Wild Bill, this may alleviate some of
my alignment and lateral load concerns as far as pump input shaft is
concerned. As far as the 283 Chevy is concerned, it is a standard bore
but high mileage motor that still works. It has to do for now but
someday, it may be rebuilt and used in some restoration project, or
maybe reincarnated as a 302. But thats a project for another time.

Now I have to figure out if the motor's peak torque output is close
enough to match the pump's effective operating range, around 1800 RPM
has been suggested as a rough estimate for the pump. I think most
Chevy's cammed for torque instead of max HP would tend to come in
around that range. My motor is stock and single carbureted, it should
be about right. I hope its right because if the motor bogs down, the
added complication of a transmission to gear down woud complicate the
power train and compactness of the skid steer. I guess I'll find out.
maximum