Off idle stumble is a classic case of too lean a mixture, or a distributor advance problem. Have the mixture measured at idle, and get it adjusted toward the upper end of the specification range. These cars were set up notoriously lean for emissions problems. Also check the ignition timing and advance mechanism. If the advance is working (especiallly the vacuum advance - check ALL the vacuum hoses), try increasing the advance setting a little bit. I think the specification is 10 BTDC - you should be able to 14 or 15 BTDC with no problems.