I gave that some thought though I would have to rerun the hookup wire between the batteries and the board and I did a fairly good job with it.

In the long run that is probably what will happen though.

That is the transmitter I have in front of me in kit form, and the associated power pack with 90V B+ should be arriving tomorrow.
My reading of the ACMA regulations makes me think that ANY AM broadcast power output is illegal, but hey let's live a little dangerously here. The key point is to keep the power so low it doesn't interfere with the neighbours' equipment, and the frequency - on which the transmitter operates - different from any on which our local AM stations operate. The only concern then would be the frequency stability of the transmitter's signal, but if the power output is kept to a minimum for in-house reception, then it should not be a concern.
Brad, your handiwork is a work of art, as well as technology. Have you an estimate/actual figure for the life cycle of the batteries? We used to live in the bush and there was always a concern that we had enough replacement batteries in the A supply on hand in case the radio failed in the middle of the Argonauts program on ABC.

I'm on my second A cell but the B batteries have some puff left in them, which is amazing since the transmitter has had several hours on it. I think the key here is the fact that those hours aren't continuous and even disposable batteries do recover slightly when not in use.

Perhaps a test is in order. I'll try and do that this week.

If American is to your taste, try this. I built one a few years ago & it works well.

http://www.antiqueradio.org/transmitter.htm

The author advises constructors to use an isolating transformer - not a problem in Australia & New Zealand - we have to use a step-down transformer to avoid putting the 117L7 into orbit. I bought a small one from Dick Smith, gutted it & mounted the transformer into the transmitter case. I don't think DSE carry these any more but Jaycar sells a similar device.

https://www.jaycar.co.nz/50va-240vac-to-115vac-stepdown-transformer/p/MF1091

Good luck!