I don't run in Nascar any more, but with the rules as they are I could build a SG+ that would be faster and more robust that the one I ran in 2010 and was very close to Roy's very quick championship-winning Life Like.
The basics are the older grey '2 dot' traction mags, .250" OD rear wheels and tyres that suit - from .418" to .430". I go a bit higher than most people.
The JL Chevy body is a good racing body and can now have an integral clip. Using Bud's SG+ clip would give you a less fragile set-up than with the stock clip.
As for internals, if you have 2 or 3 SG+ chassis, matching the motor mags would be sensible. The compass and graph paper method is accurate and cheap. Pick the best arm you've got and run it in really well. One of the advantages of the SG+ over the LL is that once it's on song it stays there.
And, as Jon said, using smaller front wheels and tires is good for front end control. BSRT shoes are a good upgrade that we use in WHO Nascar. I've not tried a G3 guide pin, but that might also get the car to stick at the front too.
Like with the Tyco in F1, building a SG+ to win in Nascar takes time and skill - but it's possible. However, running a Mega-G in F1 or Life Like in Nascar is going to be the sensible or safe option. Same with a MR-1 in Mod or a G3 in Pro.
The fact that some of us choose to run 'difficult' options makes things interesting and one of the things that makes HO interesting for me
But I'm not about to argue that Wizzard runners should have a parts advantage over G3s - I want to prove the Storm can win on its own merits. Maybe not this weekend, but one day...