Need advice with bus re-power

Eighteen months or more ago we imported a School Bus to convert to a mobile home cum hot-rod.

Here's a link to the saga.
http://www.clubhotrod.com/hot-rod-lo...s-origins.html

The body-work is now virtually finished, we've converted it to right-hand-drive, it's sitting on the Chev chassis, the panel work has very little more to be done before painting, (but that won't take place until after the the interior is completed,) and now it's time to turn our attention to the mechanical side of things.

When we brought the truck chassis into NZ it was running a 454 with 3sp auto.
I don't want an auto.
I'm a truck-driver; have driven trucks and buses for over forty years and millions of miles...with an auto all one does is 'go along for the ride'; with a manual box you actually 'drive' the thing.
It has been suggested to me that we use an NV4500 box; a five speed that will give me the flexibility I want for a three ton gvm/gvw vehicle.

Also...
The original 454 engine is suspect. It hasn't been fired in two years, but a compression test showed that some cylinders are ][I]well[/I down.
Also...
At some stage the computer has has water in it; it's a throwaway, nothing salvagable; biff the lot.

Bearing all this in mind; we've decided (after much debate,) to bite the bullet and biff the engine too...we don't want to spend some quite serious coin on the computer and then in two years have to biff (or re-build,) the donkey for more serious coin.
It has been suggested to me that we use a crate 400 Vortec, i.e. six liter.

Your thoughts please?

I don’t know about availability of parts down there or donor vehicles, but if I were building it here there would only be 4 engines I would consider. Any of the 3 455s offered by Buick, Olds or Pontiac or my first choice of a 500 Cadillac.

All four engines make a bunch of low end torque in stock form (and some REALLY impressive numbers can be had with the correct selection of aftermarket components). They are also know for their reliability.

The down side is the BOP and Cadillac share a common bellhousing bolt pattern and it is different than the Chevy BH bolt pattern. I don’t see adaptors for the NV4500 to that pattern but here a link to some posts on what it would take to make it work.

Questions about BOP bellhousings [Archive] - International Full Size Jeep Association

I think it’s doable, but it might take a bit of custom work.

Just my 2 cents.

Same availability disclaimers as Mike, but what about the Cummins drive train from a Dodge truck? Lots of torque, come with a 5 speed configuration so no adapters, wide range of fuel tolerance, and I would imagine Cummins parts/service is available in your market. And with some of the available aftermarket exhausts they sound wicked too.

Thanks for the input.
The biggest problem with running a diesel motor is that all diesels in NZ attract RUCs, Road User Charges, a tax graduated on the size/weight of the vehicle, which are charged per kilometre travelled, and payable in advance.
More bureaucratic bull#@!t to contend with!
My odometer is graduated in mph, and the RUCs are payable in kilometres...just imagine trying to explain to your average plod the disparity between the odometer reading and the RUC sticker in the window!

Mike, donor vehicles down here aren't out there in great numbers; the most common vehicles on our roads come from the land of the rising sun, and any second-hand American iron attracts a premium...which is why we imported the Chev chassis/motor/box initially...it was the cheapest option.
But the trouble with importing is that there's no come-back when/if the deal goes sour, as it has in this case; the 454 we imported as a good runner isn't, and you can't punch someone's head if they're 5000 miles away.
(Talk to the Lamin8r about this! He too got done.)
That was a big factor in opting for the crate 400; they're imported by by a Kiwi in Matamata, a five hour drive away...I know where he lives if it turns to custard.

But please keep coming with ideas and opinions.
(I guess that partly I'm trying to validate my own decisions!)