Now i've never done this job but these are a few things i would think would be different.
The wiring loom will be different.
The Engine mounts will be different
All the pipework would have to come from a 16v Integrale
Are the Radiators (Oil & Water) and Intercooler the same?
Gear Ratios / Clutch & flywheel (the box will bolt on (the bolt pattern is the same))
All the associated brackets etc
Also don't forget that you should really change the front suspension to allow for the different weights
I don't want to put a spanner in the works, but for the amount of work and cost i'd think it would be easier to source another 8v and drop it straight in?
Anyone with more knowledge than me may know better though.....