Get hold of a very late Sierra or Granada with the Zetec 1.8 or 2.0 engine and Type 9 5-speed gearbox.
They rust spectaculary but the engines / gearboxs are relatively bomb proof, are rear wheel drive and loved by the kit car world.
This would be an easy swap, needing some simple engine mount fabrication and maybe modification to the propshaft.
The rear axle could be replaced for an MGB, Capri or similar live axle if necessary.
We have the technology (and facilities) - a simple winter project.