For this booster I used "Petersen's book of man in space" that contains hundred of photographs from all Gemini missions. This book was published in 1974 and I found it in a second hand shop in Auckland , New Zealand in 1982. It must be a difficult book to find now.
For dimension, I used Peter Alway's book "Rocket of the World" which is an invaluable source of information for scaling your model, you can get this book from
PO Box 3709
Ann Arbor, MI 48106-3709
I have reproduced the sheet dealing with the Titan II / Gemini booster
Although having the dimension of the rocket is very important, it is not enough to reproduce details and I had some troubles in finding good photographs of the engine bay. I eventually found it on the web and interestingly that is how I got to the space-modeller mail list.
You can find very good photographs of the Titan II booster and its engines on the Titan II ICBM web page as well as on the Titan II page of Sven Knudson web site where are incredibly detailled photos of the booster and its engines.
An other incredible finding is the detailled drawings of the booster and the engine bay in pdf form, this really helped me a lot and I am grateful to ROBERT W. BLASKE to have put these drawings on the web.
I have not tested this but drawings are also available from Realspace on the Titan II / Gemini booster.
See these drawings : Sheet 1 and Sheet 2