well i thought id give it a go.
i dont know why i didnt think of this earlier.
i have a renault 5 gt turbo convertible as well, and tonight i thought id take the intercooler off that and measure up to see if i could physically fit one before i buy 1.
then i suddenly thought, why not use the 1 off that car, its not going anywhere. lol
so all i gotta do now is get 2 new pipes welded on the end and its ready to fit, dont even need new hoses.
its pretty much the exact size i need

the core is 500mmx180mmx60mm made by forge.
i would probably go for a 600x300x100mm from ebay if i change it
heres a pic of my pipework that runs under my engine, and said cooler
so just get 2 pipes welded on the top of the end tanks at 45degrees, and take out the 2 middle hoses and the 2 outer hoses will fit in just fine. result
i would hope that this intercooler and 1 charge cooler should work ok.
if not i can get it all in and working then see about getting a bigger IC later on.