If you're good with a spanner: replace the engine in the mint L series with another known good one - make this the daily driver.
The brumby: Fix up the body work first then go from there with engines etc. Always fix up the body as this is THE most important component of any car!
As for engine choices if you're wanting a turbo engine I'd be looking at a WRX half cut. Its a tried and tested formula that works well with a crossbred conversion. If you're looking at offroading it - at which point I'd make the brumby the daily driver

and start setting up the L for offroad/touring...
Which ever you're looking at offroading at least a 2 inch lift is a good start. Then you can start looking at larger tyres and kitting out your subi to make offroad touring a simple and enjoyable outing every time
But this is my advice - I'd love a targa brumby to do a WRX conversion on
Cheers
Bennie