Apart from the recreated songs, an original chorus and hook was added at intervals to help string differing sections together. The lyrics and a MIDI rendition of the most successful single can be read/heard here.
The first such release, Stars on 45, featuring songs from The Beatles, went to Number 1 in the US, and Number 2 in the UK, and several follow up records did well too. An album followed, featuring medleys using the songs of ABBA, Stevie Wonder and Motown, but the formula was short-lived, and a second album sold less well and was the last from Stars on 45. The format cropped up a few times by other acts in the 1980s, for example by Jive Bunny and the Mastermixers, as well as a series of "Hit Mix" albums (e.g. "Hit Mix 86", a medley of many hits from that year).
The '45' in the title refers to the playback speed of a vinyl record single - 45 rpm. Such singles were often simply called "45s" (information provided for the benefit of anyone born after 1984).