I have just changed existing Blockleys for New Blockleys, very happy with them and my advice is not too much PSI, like 24 works.
Also get the 4mm Inner tubes, tough as old boots!
Interestingly Blockley recommend running at 30psi+ which gives better precision and grip. I believe Red Three and others run as high as 35+psi
This can cause a harsher ride on the standard shocks but if you have adjustable (Spax, ATR, Ohlins....) you can soften them off a bit to compensate. I run my Blockleys at 28psi with Spax adjustable.
It's worth trying the higher pressure, you can always drop it again.