To echo others here.. in the world of model railroading you can create whatever universe you choose. It is often said in the real world that anything is possible given the time, money and manpower. In your world an unnamed benefactor (maybe a long lost relative of yours) has donated/ willed/ gifted you the money and this is how you choose to spend it. The loco can then be restored in such a way that modern technologies are used to restore the loco but details are put in place to make it look more period appropriate. For example, steam engine tender cisterns are being restored with welded construction, but are having rivet detail added so it looks like it was constructed using the accepted building practices of the day.
Your imagination is the only limit. Don’t over think it. Keep it simple as you have already stated. Hope this helps.