I have used an 1 1/4" freeze plug in the back of the intake in the past and had good results. I'm not a huge fan of the rubber expansion plug.. The baffled fittings are a great idea and can work nicely. If you so desire you could ship your valve covers up to me and I'll weld the fittings on for you and send them back. Not like I have much better things to do since my car is finished for now, lol. What type of valve covers are you running currently? Maybe we could hook you up with some nice fabricated aluminum ones???