The regulations for next year haven't been settled yet so anything I say may be subject to change but I wouldn't expect it to be massively different. A 125 Sigma would fit in class 2 or 3 depending on tyres (2 = List 1A and 3 = List 1B). The tyres thing may well change as the MSA have moved most of the current 1B into 1C which are not "road going". If it's an ex-academy car then it would be class 1 on List 1A tyres. Current favoured list 1A are Yokohama A539. Favoured list 1B are Kumho V70A or Avon ZZR in supersoft compounds but these will move to 1C for 2016. I would wait until the 2016 regulations are published before deciding on tyres. FIA bar is fine as long as you have the petty strut fitted. Classes 1 -3 fall within the MSA "Road going" class and therefore HANS is not required. Helmet will need to meet one of: FIA 8860-2004, FIA 8860-2010, SNELL SA2010, SNELL SA2005. (Not valid after 31/12/2018), SNELL SAH2010, SFI Foundation 31.1A, 31.2A. (Not valid after 31.12.2018). 2015 MSA Blue Book has all the details but there may be some changes for next year. The last introduction to sprinting day was 2014 so there may well be one in 2016 - normally around April time.