RV8 - 9.5 clutch - s1 gearbox

Hi All - new here. I've been in the process of converting my 2A 109 station wagon to 3.5 V8. At some point I realised that the 2A gearbox had been swapped to a 1959 s1 unit. I've mated everything together - but I can't get the cross shaft on the gearbox to rotate enough to properly disengage the clutch plate. New master, slave cylinders, new lines. Visibly the layshaft on a s1 differs from 2A. Does anyone know if there are reasons a s1 gearbox might not work with a 9.5 clutch and pressure plate. Flywheels is redrilled RR. I'd sincerely appreciate any help.

Is the clutch pedal travelling to the floor, or are you met with a firm stop before the pedal goes all the way down?
The piston in the slave might be hitting the circlip at the end of the bore, thus limiting the amount of push onto the clutch pressure plate. It's easy to end up with an incorrect slave (the pistons do differ) and you end up having to extend the pushrod.
I've also seen wear with elongated holes in the tubular sleeve between the gearbox and slave mechanism. This can rob you of needed clutch action.

Make sure your pedal is at the correct height off the floor. I can't remember the correct measurement but I'm sure someone here will assist with that. Also make sure your master cylinder has some pushrod free play.

Thought S1 boxes were manual(rods) clutches?
Could they have put a S3 slave bracket on it?