I honestly think that the idea of building an aluminium replica or looking at acquiring a project is more practical and most likely no more expensive.
When I got my car I didn’t know much about its construction only that I had originally clapped eyes on the one I now own in about 1975 and best part of 25 years later it was sitting in my garage looking very derelict.
When I discovered that I had bought a fibreglass monocoque I was very pleased that I wasn’t going to have rust problems etc of a steel car but fibreglass does have it owns problems and challenges which are easily equal to those that a steel monocoque can throw at you.
In theory you can do a lot of the work without having to spend ages learning specialised techniques (like welding) but in practice it isn’t quite that easy particularly if you need to get a good long lasting surface finish.