Sorry to break a bit of disappointing news, but youve not got the best cinq to work with here.
The 899 isnt a good base in trying to make faster, its possible to a certain extent, however its not as easy to mod as a 1108 sporting and the gains will not be as great.
Engine conversions are a lot more complex and difficult than with a 1108, and aftermarket parts, there are more to choose from with a 1108
Im gathering buying an 899 you arent exactly an 'older' person who will have a lot of no claims, so i would think engine conversions are out for the time being.
If i was you i would sack the 899 off and buy a sporting. A lot of other cinq owners will say the same