Being a 93, you might just squeak by with your stock programming on the L27 PCM if you stick to the L67 MAF.
Machining the 'tube' that the filament is in may slightly increase flow through the TB, but not by much....very small amount. I don't think it will allow a more 'accurate' reading. It'* really only using the MAF as a reference. The MAP and the O2, not to mention the IAT all play roles (and the TPS too, for that matter). The point is that by increasing the exposure of your MAF by machining won't gain you anything, as the O2 will be getting the final word on your AFR, and will adjust it appropriately.