Based on quite a bit of experience with SU's, albeit a long time ago; depending on cylinder head configuration and intake manifold configuration, I believe you could make either (3) H-6's or (6) H-4's work successfully.
Tuning triple SU's is not overly difficult, assuming you have lots of experience; however, it can be quite challanging if you have no experience in tuning SU's.
Tuning (6) SU's is challanging.
Give me a call during normal telephone hours, if you wish to discuss.
Jon.
