For EFI, I would not look just at megasquirt, I would look first at dropping in working EFI from a similar displacement V8 engine... BMW, Rover, etc. Early 90s EFI would probably be the easiest, as more ECUs then were standalone and didn't require BCMs and other extraneous bits. All you'd have to worry about is the manifold (which admittedly is a fair bit of worry). If you are going to install LPG, installing EFI is a complete waste of time anyway. One or the other. I assume it is unacceptable to mention that a complete engine and gearbox swap would give much better results for both performance and economy than anything you could do with the Stag engine.
