Hi Andrew,
You have four options for the SC4, the Seig 'dickson-like' one, the 000, the 100 and 111.
The SEIG one works fine, but doesn't have the simple and quick lever mechanism.
The 100 and 111 need the fixing post modifying by putting a M12 thread on the bottom, the 000 needs new fixing post, M12 below than 10mm diameter.
The 000 is ideal for the mini-lathe or Myford 7-series, but looks a bit 'lost' on the SC4 (although it works fine).
I've done some trial with the 100/111 and they are excellently made but their ability to hold larger tools means they need another tweak to suit the SC4.
My guess is that most other larger toolposts will need a similar mod.
I'm currently using a 111, but working with Ketan on ideas to customise them to suit the SC4 better.
I suggest you give Ketan or Ian a call at Arc and discuss.
Neil