im wanting to upgrade my stock mass air to the 73mm maf for the 19 lb injectors I want to know if it will work with a k&n conical filter with a c&l shield with the stock tubing from the tb to the maf will I notice a difference with that maf compared to the stock maf on a mildly modded 5.0
The stock MAF is a restriction. The larger MAF might allow some additional rpm for a tad more top end power if everything else is tuned right. Whether you use the stock or aftermarket MAF, either setup would work better with the factory air box (spark arrestor portion inside fender removed). You can get a K&N element for the factory box. There's plenty of discussion on how the conical filters attached directly to the MAF or with short adapter do more harm than good. They cause troublesome turbulence, not to mention you are pulling hot under hood air.
I wouldn't spend much money upgrading a MAF for 19lbers. IMO go to any JY and pull a MAF from a 94-95 GT and it will swap right in. They are 70MM from the factory. The only thing you need is to either buy or fab a bracket to adapt it to the tube. It's a cheap and proven upgrade, which I have on my car now.
I personally used the 73mm C&L for many years, and never had any issues with it. Started out using the 19# calibration tube, and later switched it out to a 24# tube and it worked flawlessly both ways. The factory 70mm is another option.