At an emotional crossroad

Woody, DO NOT sell the car. You'll regret it for the rest of your days.
In regards to the engine, you have answered your own question. If you can't swing it financially, then you gotta look at another option. You will waste years collecting "one piston at a time". If you go with an LA motor and get her on the road, you'll have those years sitting in the driver's seat. Not staring at the car in your garage, desperately wishing it was finished. Build it!