Low compression after wiseco kit

I just put the Wiseco 810cc kit in my '82 GPz 750.

Getting the cylinders over the pistons was a major bitch. I think the
machine shop that bored the cylinders didn't chamfer the sleeves at the
bottom enough, as the cylinders would happily slide over the first two
rings, then hang on the very bottom oil ring. Eventually I got them on, and
everything seemed okay, until I got the motor buttoned up and checked
compression.

Cylinders 1-3 are just fine, but #4 doesn't seem to have much, if any,
compression. I can hold my finger over the spark plug hole indefinitely
while cranking the motor with the starter. Cylinders 1-3 blow my finger out
immediately. That's not good for #4.

It's *possible* that during the grunting and swearing period of cylinder
installation I *may* have let the top and bottom ring gaps align. *Maybe*, I
don't think so, but it could have happened. Would this cause a total lack of
compression? Those gaps are pretty small (0.004). I could see a drop, but
none?

I'm looking for alternative causes to rings here. I really don't want to
take the cylinders off again. Could a piece of carbon be holding open a
valve? Any chance in hell this problem will solve itself during the break-in
period? Anyone had this happen before?
    The bike ran fine before I tore it apart. All valve clearances were at
the loose end of the spec, and I'm sure I got the cam timing right.

I'm almost certain the head is coming off again at the very least. Damn it.

TIA

Dave G.