If you go to the Literature section of the web site, there are some price lists that list various I/O options. I had a 1972 Seafari 20 and it had the 140 Mercruiser. However, they offered the 165 Mercruiser, as well as the 225 and 245 OMCs in 1974.
Thank you kindly, sir.. Are the 165 Mercs and the 225 and 245 OMC 6 cylinder blocks or are the OMC the small Ford V8's?