Look up the wiki between differences of H89 (closed chamber) which is superior head for performance to the H75 (open chamber)- Higher comp engines have been successful with bigger turbo on 6-8lbs boost so the A14 should with a .6X rear housing by the sounds of it since Nicks setup cam nicely at 2600rpm. Nick what was you front housing? You probably should go for the 1.75 inch SU or Stromberg for more fuel and air to feed the sucker as TopGear has done in the past and others, one in a datsun 1000 wagon is pushing 30psi with 1.75 inch SU and crude water injection which blew his boxes apart then upgrade to Escort 2ltr pinto 4 speed box cut and shut bellhousing and now the toyota T50.

A14 pistons are a little thicker up the top than the A15 pistons so a little more strength while rings are all pretty thick strong items for all A series.