I have a question I would love for someone to have a stab at before I
tear this motor out.

I have recently transplanted a running engine into my 72 mini, and now
when I try and fire it up I get nothing. The trouble is, when I first
started cranking it, I forgot that I had drained the oil. So after a
minute or two of cranking I put in the required amount of oil. But, as
it did before I put the oil in, the engine seems to turn over very
fast, much faster than usual, almost like there is no compression going
on. All cylinders read 120 psi compression. When I do the compression
test, with all plugs out, the engine spins at a slower speed on the
starter motor than it does with all plugs in and trying to start...

The dizzy is an old one I have, worked in the past but with a new set
of leads and a new cap and rotor. Bought from the local guys, not a
hundred percent sure they have sold me the right stuff. There is a
spark going on but I would describe it as small and yellow, not blue.
The battery is new, and holding 12.8 volts sweetly. What colour should
the sparks be, and can you have a dizzycap/leads that will kill the
power of a spark even though you still get some spark at the plug?

I am a little worried about the oil.