1970 Squareback Running on 2 Cylinders: New Engine?

[manfred]

I have a 1970 Volkswagen Squareback. The odomoter reads 63,000....but I have a feeling it has rolled...at least once. Previous owner claimed no...but that might have been an evil plan to get me to buy it.
Right now it is running on 2 cylinders. Cylinders 1 and 4 are not firing.
I understand that this is not a problem to do with the points, because either 1 and 3, or 2 and 4 would be a missing pair, not 1 and 4.
I don't know what to do to fix my problem.
The symptoms of the situation are, lugging, top speed of maybe 50mph, problems starting, slow warmup, missing, and backfiring.
I am currently parking the beast.
Do I need to put a new engine in the car?
What would it cost to put a rebuilt engine in it?
Is it possible to find a Porshe rebuilt engine instead? How are they compatible?
Thank you for any comments you may have about my situation.

Mandy