going LHD!
Well, after more thought on the full scope of work needed to the cab, I decided that I would look for a cab firewall that would fit - and be LHD. Fortunately, another 'Mudder on this site, Seapotato, had exactly what I needed. And he gave it to me (thanks!) so it worked well with my current finances! Hopefully I will be able to help him out with something one day.
Got the bulkhead into the back of my Mazda 323 and brought it to the shop. I've aleady drilled out a bunch of spot welds and have removed the vestige of the transmission hump sheetmetal. Yeah, I know, pics would be nice

Trying to decide exactly where to slice and dice is the next consideration.
Now I need to find the heater ducts to work, and a heater I believe, maybe the blower too, and steering gear (lotsa decisions to consider with that especially, though I will definitely be going with a power steering box. I'm considering using my 60 series steering linkage, as it is beefier and could undoubtedly be modified to fit properly. I would love to keep the current '84 vintage dash, but I would need to find a LHD donor dash from a 1984 - anybody have something like that kicking around their yard?
Then there is the windshield frame issue with the reversed wiper arrangement - maybe I can cut out the lower sheet metal and reverse it 180˚. Has anyone tried that?
The wiring harness should be fairly straightforward to reconfigure.
I have a bunch of photos on the camera that I will try to post up in the next few days.
With the firewall to retrofit, I can feel a little overwhelmed sometimes! Just remember to breathe and be confident...
Cheers.