[JasonB]

Here's a quick rework with the flat junction. One or two borders would need to be trimmed a little to fit the 8x4 footprint.

   

I feel like I should add a note of caution here though, as I honestly feel like this sort of track will be quite unlike most other tracks you'll race on, with the predominance of tight R1 corners.

As Chris said, a routed track would be great, but if you're anything like me, you probably don't have anywhere to make one.

But looking at the tracks above, I just wonder whether something like SCX-5015 or SCX-5112 might make a better test track? They might not be as visually appealing, but they have a much more even balance of corners. You could replace the flat R3s on the left with banked R3s, which would give you a nice high speed section round the outside, and you could replace a couple of the R2s with an R2 crossover curve, so that you drive both lanes, and therefore test your cars on every radius of corner that Scalextric have to offer. Just a thought.

Let us know how you get on with SlotMan. It's ages since I used it, and I'm so used to using UR that I found it difficult to change my habits.