I'm trying to plan out my weekend and upcoming camping trips and am
trying to get a feel for how much time I'll have to spend to get my
van back on the road.

I have a loud clanking sound from my engine.  It's not the tick from
lifters.  It is considerably louder.  There definitely seems like
metal is rattling around.  It appeared to sound  like a nut was
rattling in the exhaust.  (I don't think there is one, but it sounded
like this).

The problem occurred 30 miles from home last weeknd and I drove home
on the freeway with the loud rattling sound.  No power loss and no
drivability problems.  However, the sound is really loud.

Joel Walker was kind enough to suggest that one of the pushrods might
have come unseated from the lifter.  This situation is possible since
I just changed two lifters about a month ago and had the pushrods out.
 Also, I adjusted the exhaust valve on cylinder 3 considerably.  I had
a problem with air in the lifter and the valve was about 5 turns too
tight.  So, I loosened it up so that it was barely touching, then
tightened it down about 1 1/2 turns.  I wonder if air was still in the
lifter and somehow the pushrod became unseated.

I may not have time to take out the pushrods until the weekend.  If a
pushrod is unseated, what else should I inspect for damage.

Also, do other people suspect a pushrod?  The problem began while I
was driving on the freeway.  I continued driving for another 30 miles,
so I don't think it's a valve clanking around in the exhaust.  I took
off the u-pipe for the exhaust and there's no metal in there.

My friend wants to drive up to Lake Shasta in a couple of weeks and
I'm planning the trip, assuming I'll be able to go.  However, I
obviously won't go unless I resolve this engine problem this weekend.