If you are not sure what sax you have, an alto is about 25 inches tall and a tenor is about 28 inches tall. The serial number list here on Saxophone.org shows that the Imperial serial number you report is a 1935-1936 model. It was considered a professional horn (unlike athe Imperial models that Martin brought back much later). You can find some information and pics on the following sites: http://www.saxpics.com/?v=mod&modID=81 http://www.doctorsax.biz/martin_old_imperial_1032.htm
The Handcraft Imperials were in production for a relatively short time. I agree that there is only limited information available. The closest I came to any analysis of the horn was a review of the general Handcraft model on the following website: http://www.shwoodwind.co.uk/Reviews/Saxes/Alto/Martin_Handcraft_alto.htm
He does a very thorough review of the horn's physical and playing characteristics. The Handcraft Imperial was a little different than the original Handcraft, but the general characteristics will be close.