Over the years I have ported multiple products from older 8051's over to SiLabs parts. (In fact the first port I did was back when the company was called Cygnal.

In several ports I actually made small adapters to allow the SiLabs surface mount parts to be adapted to the original product's MCU socket so that I could do the software development (or porting existing code as necessary) with the actual product hardware before committing to the new product printed circuit board artwork.

One example of such an adaptation can be seen at the following link. In that case I used the SiLabs adaptation just for software development and debug and never did redo the PC boards of the product since at the time the customer had a huge number of MCU parts in stock.

http://carousel-design.com/SiLabs_ICD.html

Michael Karas