[JP Noonan]

The actual Porsche ones are good, there are a million junk Type-I swivle foots out there (I guess some good one too). However, the big thing I've heard that unless you use spacers and/or change the pushrods the swivel foot messes up the rocker arm geometry. Look how the stock rockers sit fairly close to the vavle, with the swivels they are further away.

I can't say from experience with your conversion, but from erperience building motors in general, part of the assembly process is to check rocker are geometry (because if you use the old vavles, the heights can change, different cams like roller vs. flat, also change it).