i am doing a 3.4L swap now. turns out the E39 BMW 540i has the same diameter MAF housing with the same type of MAF flange. it's like 84mm inside. i bought mine off someone on bimmerforums.com for $40. the guy with username 92535i92 has five of them for $20 each, shipped. it's 3.5" OD.

i've been working with cloudsurfer on the overall intake design. he bought the Cayman S MAF & housing, which is similar in size / design to the BMW version (but a lot more $$$). he then routed some silicone hose to the MAF housing & installed a BMC in-line air filter.

FYI, this is the same route i'm taking. the BMC was like $215 (shipped from Italy).

i haven't installed everything yet; still waiting on lots of motor parts. if you look for my 3.4L installation thread, cloudsurfer posted a pic of his setup. very nicely done.