Hi,
Further to Longbuilds post, a well known model yachter, Bob Jeffries, ran a series in the Jan-april 71 editions of RCM&E magazine on an "Introduction to RC yachting". This used the Starlet as a basis and is well worth getting hold of if you can, particularly the Feb edition which contains details of the worthwhile improvements that he made. While this was particularly based around the electronics of the time, he did increase the size of the rudder by about 50% and increased the size of the keel fin .
My father and I were inspired by the article and built the Starlet with the improvements as our first boat with RC ( McGregor Codamatic single channel !) . We later upgraded to Horizon 2 channel proportional and had many happy hours sailing. Still have it tucked away awaiting a winter refurb.
If you can't find the original Model Boat issues, the details were reprinted in a paperback A4 booklet entitled "Simple Model Yachts" by Vic Smeed which occasionally comes up on Ebay. I have a copy somewhere, if I can find it, I would quite happily photocopy it for you. Up until 2010, Model Boats not only sold the plans but copies of the magazine articles from 66/67. They were A4 copies of the double pages of the magazines , so were quite small copies. I have set of these somewhere but MB do not appear to still print these.