Just use the original 235 clamp, it works fine and gives you vacuum advance using the original hardware. If the distributor comes with vacuum advance, you can use a non-vac advance clamp from a GMC 270/302 distributor.
Also, the early S10 HEI's are the mini style that works well with a low resistance standard coil (pertronix 0.6 ohm Flame Thrower) mounted externally for a more original look.
