I think I might be getting somewhere! I have found PR engine numbers in this list:
https://hotrod.gregwapling.com/chev-...dian-chev.html
It shows the PR series as being assembled in Australia. If I understand it correctly my number is in a series of engines assembled in Melbourne (starting from PR3849349) This shows the engine was in a C60S (Model 2844200538M)
Grateful if someone can confirm my theory!! If right at least I know its a 216 engine block!!