I am the guy who did the damage to the rodcap with a misplaced lifter.
BUT: There is no way a lifter can get into the crankcase with the camshaft in
place. My lifter fell in with the camshaft out. And the reason it did fall is
that OEM lifters are almost impossible to pull up and out of their bores in an
old engine. They swell on the bottom end (some call it mushrooming) and it is
rare that you can pull one up and out. If your head is in place I would guess
that your lifter is also in place. Better check again.... Even if it did come
up and out it cannot fall into the crankcase and probably could be manipulated
back into place with sufficient animal cunning and manual dexterity. BTW I have
run several engines with as many as 5 lifters in the crankcase and only had ONE
case where there was damage because one did not fall all the way down when I
thought/hoped it did. I was replacing a B30 camshaft and lifters at my daughter's
house in Tennessee and had no way to pull the engine or the pan. I ran the engine
another 15000 miles before it caught up with me at San Simón, Arizona. But that
(as they say) is another story or three.....

But if you have to replace the headgasket anyway, why not pull the head and
see what is going on in there?
--
George Downs Bartlesville, Heart of the USA!