In 1996 I was given 2 beautiful, 2 lane, professionally built wood tracks that had the guide strips with a 4" center to center. I equipped them with Microwizard timers. They served us well. A few years ago I bought a 2 lane Best track. The Best track has 3 1/2" centers which leaves about 2" between the edges of the guide strips. I made a simple mount for the timers to line up with the end of the Best track. I use only one lane for my personal business so that particular timer hole is offset a small amount. This works for me because all my cars are Hershey bar shapes so they have a full front end. This would not work for a very narrow front end. That is why the cars run a full 30' from Pin to timer on my track instead of 29'10" on a 35' Best track.
There would be advantages if you move the 2 outer strips so you have 3 1/2" centers. Your scouts can practice staging on what they will probably face on regulation tracks. If you decide to buy a timer to serve all 3 lanes and later decide to buy a Best track, you can have Best track punch holes at 29'10" and you will have a duplicate of what you might be racing on at Pack and District. If someday you decide to sell the package I think it will be easier to sell with 3 1/2" centers. Timers are sometimes For Sale on Derbytalk for reasonable prices and they will have 3 1/2" centers. If you decide to time only a single lane then most of what I have said is not important. I think it is important to set it up for your scouts so they can practice staging on those close lanes.
There are 2 - 4 lane Microwizard timers for sale. Each is $125.00 including shipping. If you read about all of Microwizard timers one of these timers might serve you well.