Here's the fourth page (page thirty) of the letters column:
(Click
here for a 1328X1996 version (without any of the artifacts that the forum's system created when downsizing the image))
More Book 1, Issue 4 comments - and a theory as to whose image Uncle Vincent might have been based on. However, you'll have to wait until the fifth page of the column to get some info about whose images were in the running to be used as Uncle Vincent and whose image he was ultimately based on...
Also, note that the images on this page are from Pages 19 & 20.
The images on the fifth page of the letters column are from Page 12, so, unlike how there was a gap of over a month between the posting of the third and fourth pages of the column, the fifth page will be showing up sooner rather than later...