I use 20 to 21psi all round with the same size tyres on my Moss box Plus 4.
As Tim says, heavy steering can be due to a number of factors. The steering is always going to be heavy at parking speeds due to the combination of radial tyres, the heavy Triumph engine and the Cam Gears steering box, but it should lighten up once you are on the move.
Check the front wheel tracking.
When greasing the front suspension, it's important to get grease into the area between the steering damper plate and the top of the stub axle. Jack the car, use a large blunt screwdriver with a hammer to prise the damper plate away from its seat on the stub axle and this will allow the grease to travel through the grease nipple into the cavity in the stub axle and then out through holes into the area that you have prised open. Terry Foxen at GEE Ltd taught me this.
