The Jackdaws Castle handler is chasing a third victory in the race having sent out Mini Sensation to claim it in 2002 and subsequent Gold Cup winner Synchronised in 2011.
After picking up a novice handicap chase at Worcester on his penultimate start, Upswing turned in his best performance to date over fences when chasing home Sausalito Sunrise in a Grade Three event at Cheltenham last month.
O’Neill said: “We decided to go for this race after his last run at Cheltenham as he jumped and stayed very well and he fits into this category of race well.
“The ground we don’t know about, to be fair, but I’d think he would go on it as he won on heavy up at Carlisle.”
Nigel Twiston-Davies is no stranger to success in the race having won it, like O’Neill, on two previous occasions, with Earth Summit (1997) and Bindaree (2003).
This year the Naunton handler relies on recent course winner Tour Des Champs and Cogry.
He said: “Cogry ran a very nice race at Cheltenham first time out, in another few hundred yards he would have won – I was delighted.
“He loves heavy ground, stays all day, despite being only six, and must have a good chance. Getting a win out of Tour Des Champs was very good after all that time off. I’m not a believer in the bounce theory.
“He likes the track and must run well.”
Last year’s winner Emperor’s Choice will bid to become the first horse to win back-to-back renewals of the Grade Three prize since Bonanza Boy back in 1988 and 1989.
Trainer Venetia Williams said: “Emperor’s Choice is heading back to the Welsh National and is in good order.
“He is very well and this was the obvious route to take with him after his last win, but he is in good shape.
“It was a good comeback win at Haydock, although he does pay for it by coming back to Chepstow with more weight. But I am happy with him and the ground looks like it will be in his favour.”
Williams also runs Saroque and said: “The same comment applies for Saroque. He has not run over this sort of trip before but he has indicated in previous runs that it shouldn’t be a problem.
“His run in the Rehearsal Chase at Newcastle is working out well.”
Having watched Benvolio chase home Emperor’s Choice in the extended three-mile-five-furlong prize 12 months ago, champion trainer Paul Nicholls, who will also saddle Black Thunder, is hoping the eight-year-old can go one better and exact his revenge.
He said: “Benvolio had a day hunting the other day to freshen him up. He loves bad ground.
“We’ve aimed at this, he’s had a couple of uninspiring runs, he just needed a mile further than last time.
“He’s coming back to himself and hopefully a day hunting will have brightened him up. He’s in good order but he has to improve on what he’s done this season.”
Nicholls added: “Black Thunder was running a solid race at Cheltenham at the Paddy Power meeting until he made a bad mistake two out. He was a little unlucky, he may well have been placed.
“He loves the mud but is going to carry a lot of weight because he had a very successful time as a novice chaser. He’s a nice horse, but he has 11st 12lb which makes it virtually impossible.”
Mountainous will attempt to repeat his win in the 2013 renewal of the race when trained by Richard Lee, although he is now handled by Lee’s daughter, Kerry.
She said: “He is very well and I am very happy with him. He will have to carry a bit more weight than he did when he won the race before.
“He will like the heavy ground and I am happy for it to rain as much it wants at Chepstow!”
Colin Tizzard is enjoying a fine run of form and he fields Masters Hill, who will be trying to bounce back from a disappointing run at Newcastle last time.
He said: “Masters Hill was not 100 per cent at Newcastle, but he ran a solid race the time before. The way he runs looks like he is a typical stayer.”
Although Shotgun Paddy failed to complete in last year’s renewal, trainer Emma Lavelle is confident the eight-year-old will be seen to a much better effect this time round.
She said: “Shotgun Paddy is in great order. While the odd one that has come out means that the weights have gone up slightly, I am happy where he is at.
“I was delighted with his run at Cheltenham and he came out of the race really well. Hopefully things will go to plan this year as it’s fair to say they didn’t last year.
“He ran his race after galloping into the first couple of fences so Leighton (Aspell) did the right thing and pulled him up. I am really pleased with how he is in his mind and physically he seems better than last year.”