[Positraktion]

Just a couple thoughts here...I am a GREAT believer in process of elimination by simpliest methods first.
1-My Sunbeam Tiger used to do exactly what you are saying, it was due to vapor lock. But as I said, do the easy stuff first.
2-Check vacuum at idle normal temperature and then when it heats up. Get it hot so that it does stumble and see what the vacuum is.
3- Throw a timing light on her when she is at idle normal temp and then again when she is stumbling hot.

One of these tests should tell you what she is doing.

Keep us updated......Posi.....