I have a free-floated Colt HBAR-II  post-ban upper that I plan to scope and use for varmints.  It currently has a Bushy BMAS 3-rail gas block.  I never really liked the set-screw attachment anyway, just more trouble when trying to align front & rear sights/ sighting in with irons (does anybody make one that uses the taper pins?)Bushmaster's "shaved" front sight base looks good for what I plan but I don't see that they sell it separately. Does the type of gas block or the way it attaches affect accuracy to any degree?    

To address your question on accuracy, just look at the front sights on a space gun, you'll see that they are almost all clamp or set screw types.