Sometime soon i hope to do some TB work, cleaning the MAF, the TB, and hopefully a new gasket. However I got a spare L67 TB, and i'm wondering if it fits, which MAF should I hook it up with?

You have a funny problem. The L67 MAF would be for a higher range of flow, so it would make sense to use that, but your PCM may not recognize the range. The L27 MAF may not read high enough for the increased flow (assuming your head work actually uses a significant amount more flow). In either case, you'll need an AFC calibrator. Just keep them both and try each.

I'm assuming it'* a Series 1 L67 TB? What year?

It'* a 93 i've got. So it'* nothing too crazy.

I was also wondering what is possible with cutting up the MAF housing some, so it'* more exposed, ALA LS1, etc.

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.

I was thinking for flow purposes. I don't have air being suctioned in at crazy volumes so I need all the help I can get I'll check it out some when i'm looking at it.

you can always test on your old one and then if you like it do it to the L67 TB.