Yup - what Roger said. My thought with 3.73 was they are still "fairly streetable" while 4.56 will certainly introduce you to God when you hit second at WOT. Personally, I'd have a real stout 12 bolt professionally done or a Ford 9" if I were going to run anything higher than 4.11 as everyone I have ever known with 4.56 can't resist the urge to look to their first time rider and say, "hang on and watch this!" You'll also go through a lot of tires!
It sounds like you've got a sweet ride - would like to see some pictures. And it's okay if you're not the fastest one on the block. You know what you've got so cruise and enjoy the daylights out of it. I had a '57 Corvette in high school. It was untouchable until the day some rich kid showed up with a brand new '66 SS 396 Chevelle and whupped me real good. We had words, might have scuffled a bit and he left but my wounded pride stayed around a long time until I realized that I just really loved the Corvette and that was that!
Your ride - do as you want but my two cents says stay away from nitrious. It belongs at the dentist office. I think Asian imports and those who are Fast and the Furious wannabe types. I love the smell of nitro at the drags when top fuelers or funny cars run but high-octane pump gas is what hot rodding is all about. Again, just my opinion..
Best,
Glenn