McKay said he has lost count of how many vehicles will be on display in the event, which will have prizes, giveaways and raffles.
A swap meet and run will be held on Saturday from 8am to 12 noon followed by a cruise, while a "show and shine" will be held on Sunday from 10am to 2pm. Racing legend Greg Murphy is expected to be at the show on Sunday from 11am to 1pm.
It has taken a lot of effort during the past six months to organise but it was all worth it, McKay said.
Entry will be by gold coin with all proceeds going to St John.
"Firstly, St John needs the money. Secondly, downtown Tauranga needs action and entertainment to bring people to the area. That's what we are doing."
McKay admits the St John aspect was something close to his heart.
"I'm giving back what they have given me - so much help.
"I was in a wheelchair for four and a half years ... They were picking me up weekly and taking me from my home to the hospital. I couldn't walk and they were so wonderful.
"They need the money. It's a shame they are not fully government-funded, they should be."
McKay is back on two legs now but remains "incredibly passionate" about helping the charity service. And he's doing it the best way he knows how.
McKay spent 10 years as a caretaker for Baypark Speedway, which was where his love for motorsport began. Since then he has made friends and contacts in all the right places to enable him to pull together such support for this weekend's event.
The show will be the second version of the event, which debuted last year, raising $8200.
McKay believes this year's event will be far superior and he hopes to raise $10,000. Yet he admits he was surprised at how much support he has received from businesses offering sponsorship and prizes.
"I know Covid-19 has done a lot of damage to businesses ... It's unbelievable how many have come out of the woodwork and some sponsors are already booked in for next year. It has been absolutely fantastic."
McKay was also grateful to Tauranga City Council and businesses on The Strand which had been "incredibly helpful".
The event will host demonstrations including one from two trucks lifting a house in tandem on Sunday and cheerleaders each day. Live music from the Red Fox Duo and Blaze will be on at Masonic Park as part of the event and a kids' ride involving mini Kombi vans will also be on offer.