The Augusta's seats - will have to work out how to post pictures - have an exposed tube along the top of the back rest perhaps as a grab handle for rear seat passengers. The backs are plain, seats fluted, with little adjustment levers next to the tunnel to slide back and forth. They're a lovely design but the (red) leather and stuffing is all shot. The "bedsprings" might be ok still. Looks like they tilt against a spring action, but it could be a spring loaded catch.
In our MG Midget I use plywood side plates between sill and seat and seat and tunnel for additional support cornering. They're padded and covered in black vinal to match the seats. I expect I'll end up with similar for this car. Have you seen Aurelias with padding on the doors? I came across a picture of one recently - if only I could remember...
Aprilia engine into an Augusta seems to be a popular idea. The tight spot is between the inlet manifold and steering box. The other concern is how the gearlever, handbrake, and dash interact. If it came to it I could make a remote for the gear change but it would be a shame to give up that direct connection.
David