Take a look at page 20 of the following PDF document from the XESS web site. They manufacture a board with an 8051+FPGA in a pre-assembled kit, with full schematics.

XS40,XSP Board V1.4 User Manual
http://www.xess.com/manuals/xs40-manual-v1_4.pdf

As an aside, if you would prefer an integrated high-performance 8051 with integrated FPGA-like programmable logic, a high-speed bus, memory, DMA, JTAG debugging, etc., I would recommend checking out the Triscend E5 device family.

http://www.triscend.com/products/indexe5.html

[See also ...]
http://www.triscend.com/offer/specialoffer.asp