It seems like if you found a D70 for a great price and upgrade the boiler would be an option.
I found this built model of African Queen on ebay, I believe it is plastic hull with wood decking and non functional steam engine. Plastic models are often converted to RC but I suppose some extra care would be needed to protect from the heat of steam power, a wooden boat is better suited to take some heat.
The model in the ad is built, the kit can be had for less $
Just throwing out ideas
Update: the ebay ad "claims" hand built wood hull, however I have found kits that say ABS hull with wood decking so I do not know if the ebay ad is correct?
Here is a photo if the ebay ad goes away
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