Mark-

Take it easy, there. No need to rip the motor apart.

Drain out a quart of the oil, and add a quart of Marvel Mystery oil. Drive
it for a few hours. That will almost assuredly fix it.

If it doesn't, Drain half oil the oil out, and top it back up with 2 quarts
of automatic transmission fluid. DO NOT DRIVE THE VAN WITH THIS BREW IN THE
CASE. Allow the van to idle for 15-30 minutes, and *gently* rev the motor a
bit from time to time during this. Drain the case, change the filter, and
smile at the smoothness. The ATF has a LOT of detergent qualities, and will
dissolve almost any crud on the lifters.

Finally, if THAT doesn't fix it (unlikely) you don't need to disassemble
the case to R/R the lifters on an '81 van. You can remove the pushrod tube
and pull the lifter out. No sweat.

Happy motoring,
G. Matthew Bulley
Bulley-Hewlett & Associates
www.bulley-hewlett.com
Cary, NC USA
888.468.4880 tollfree