Those pictures are of 2 different machines.
Fitting a heat exchanger is simple for a competent metal fabricator, it's sourcing the actual exchanger which will be the problem, you could import one from the USA. What van do you have as it must be small if you cannot fit a little giant,.
If I'm being blunt it's a Bit daft buying a truckmount with no heat source, of all the machines you could have imported you went with one that has no way of heating the water