I think there was a set of plastic tracks from Gum Ka (You can find the review in PMMS), but they might be difficult to find by now, so the Friul tracks are your best option. I think Italeri/Revell's Crusader tanks are very nice. I have the Mk.I Early, from Italeri. It has some time around but still nice and the only Crusader Mk.I Early out there. IMO, a PE set wuill be enough for your Mk.III (If there is any available). The only think I know to be added to all of them is some missing bolt heads on the hull sides, something totally useless is you are going to place the sideskirts in place. I don't know about any other improvements, there are very few publications about the Crusader, and nothing with very detailed pics or drawings, AFAIK. Good luck. Best regards.
José.