Be careful ! IDF's are a down draft carb ! not a side draft!!
I have never seen a manifold for an IDF, although I recall that Bill Blydenstein used a big ol IDF on his full race engines - but needed a bonnet bulge to fit. Also, you can only use one on an OHV engine.
Could work well on a OHC, but again the manifold is the problem.
Cheers
Tony
"Ere look - thats one of them Mk2 Vauxhall Cortinas....!!"