The plenum is only a PITA the first time you pull it, so if you are swapping them out you have already paid the dues...Pull your plenum and do your coolant and vacuum bypasses and you will be in good shape. Have your extra plenum polished or powdercoated while its off. If you were going to pay someone to modify your plenum and go through the trouble of swapping them, my advice would be to get a set of new injectors from Bernie: [ http://twinturbo.net/nissan/300zx/forums/classified/view/155066/TwinTurbo-or-NA-New-Style-Injector-Drop-In-Conversion-Kit.html ] He can hook you up with what you need, Nismo 740's for example, and all you would have to do is swap them out for your current rails.
-___________________________________________________________- 
|