This reply is also late but can give some informaton to others I hope.
1. Make the replaceable inserts taper (easy to install), as if installation is from front side without downloading the mould.
2. Design the fixing method. Screwing method is ok -- This is also from front side
3. Ejector pins & Runner location should be exactly same
If anybody needs a sketch let me know. I will draw a simple one & send you
Vijay
http://www.engmatl.com/