I do not know how to tell the difference between Parker Hale models 1000C, 1100C and 1200C, if it is not in the original stock. There might be a way to do so, but I do not know what that is. I have a Parker Hale rifle here that I "put together" - is chambered in 308 Win - was three separate purchases on CGN - a barrelled action with the bolt and lower metal pieces, a stock and a detachable magazine. All "fit" together and function fine - but I have no clue what model it is. Triggers used to be able to be purchased separately - I have bought "loose" Parker Hale triggers on CGN.
It appears that Parker Hale used the Italian company SILE to make stocks, if they did not use former military stocks - has been at least a dozen examples examined, and all are stamped "SILE" inside the stock - under the metal - but I do not think any particular stock was marked to belong to any particular action. It does not appear that the serial numbers were used in any understandable order - they were NOT used sequentially - and is various letters as pre-fix on various PH receivers - the serial number might have been stamped there by the receiver maker when it was made - which was NOT Parker Hale in England.