Rated a $7 chance with Sportsbet, the Caulfield Guineas winner will carry the equal-lightweight for the weight-for-age championship with 49.5kg alongside maiden Shamus Award.
Top Darley jockey Kerrin McEvoy has been tasked with shedding several kilograms in just days to maximise the benefit of Long John getting the 2040m trip at Moonee Valley.
And ahead of his bid to win back-to-back G1s, Long John will not be Derby bound on Saturday-week.
"Win, lose or draw this will be his last start this time in," Snowden confirmed to Radio Sport National.
Snowden said he was happy with Long John's lead in to the Cox Plate, given the cushy run he had from hoop McEvoy in winning the Guineas on October 12.
When asked to compare his lone Cox Plate chance to former runner Helmet - who also won the Guineas before placing eighth in the weight-for-age race in 2011 behind Pinker Pinker - Snowden said it was apples and oranges.
"These are two different horses completely - Helmet and this bloke (Long John) are absolutely as wide apart as you can ge," he said.
"The only thing in common is they both won a Guineas.
"Helmet's run (in the 2011 Guineas) was a really hard race, it broke the track record, he did all the work on soft (ground), it was a hard run.
"This bloke had a soft run, was given a great ride, didn't spend a penny until he got to the corner and he was good late - he didn't win by a big margin.
"He's a winner, he tries hard, he keeps lifting... 49.5 kilos on his back should help a little bit."
On Friday night, Snowden has Sessions - a $17 chance with Sportsbet - running in the G1 Manikato Stakes (1200m) and he said going off his last start in the G2 Gilgai Stakes (1200m) at Flemington earlier in October.
Sessions was beaten 1.1 lengths down the straight in the Gilgai, with Platelet claiming race honours, and Snowden said his four-year-old over-raced.
"Yeah I thought there was a lot of merit in it (his run in the Gilgai)," he said.
"What happened to him was what I thought might happen - he just drew a gate where he just didn't get cover.
"He definitely didn't get cover, and he over-raced quite badly and he did that right from the get-go, 50m out of the gates he was up outside the lead and pulling.
"And he pulled the entire trip and only got beat a length.
"I can see him getting a good run, use that bit of cover.
"He's two pairs, three pairs back, switches off which he normally does when he gets that.
"It's a good field, he's a good horse and he just gets the good run tomorrow night."