what i plan to do is produce an fpga version of the 8052 which has 16 bit extensions ..... If anyone fancies giving a helping hand ive got most of the code written it just neds finishing off.
Have you had a look at the Philips XA, It is GREAT. They took the route of being "source compatible". Intel, because they wanted to be "object compatible" cane out with the mediocre 251.

Not telling you what to do, I still will say "do not get lost in "object compatibility"

Another issue will be that if you mimic one of the "16 bit '51s" 251, XA, 16x you will be able to compile the code. This, of course, is stated under the assumption that you do not want to add writing a compiler to coding the FPAG.

Have fun,

Erik