By 'Kennet Valley', I assume you mean the Berks & Hants?
Most of the original Mk3 electrification used masts with 152x152 UC sections, which have now been withdrawn from new installations as they tend to succumb to torsion and twisting more quickly than those with larger cross-sections. 203x203 UC is now the accepted minimum.
Additionally, in order to minimise pantograph hookover risk, mid-point anchors on 2-track sections (and 3-track, 4-track etc.) have moved away from being a single track cantilever with a tie wire anchoring it at the spans either side of it (Figure A), to being a portal over those lines where the catenary is
directly anchored to the boom. Likewise, terminating anchors now tend to be formed of those Tensorex portals to eliminate the need to cross the catenary at every overlap for the same reason.
View attachment 76841
Figure A (Contact wire Stagger omitted for clarity)