with the car being your Dad's, and that attatchment,if you're wanting to make a bunch of HP, I'd do like Big said, and stash the original engine, and get another to build. now, how are you planning to use your car? I drive mine everyday in nice weather. I always drove my cars alot,(especially after sitting all winter) but after i lost my last car in the fire, I'm more determinded to drive it. and, we all have only so many heartbeats. I know some guys around here, with beautiful mopars, that rarely, if ever come out of the garage. with the $4 a gallon gas last summer,if I had a big HP engine in mine, it would've sat. as it was my car was alot cheaper to drive than my 4x4.
Now, if you're planning on a weekend fun car, that won't matter as much.
but rebuilding the engine is just one of the normal steps in redoing a 40 year old car.