Suggestions welcomed

Thanks for your time jpar, I've read hundreds of your post on numerous topics and while I'm no expert, it's obvious that you're one of the more knowledgeable active members on this site. Honestly, all I've been doing since I got the car back in February is reading and more reading. Partly because I'm not yet financially able to do much of anything with the car and also just to aquire as much information as I possibly can. While I'm always the first to admit I'm not a mechanic I am old enough and smart enough to realize that not every thread I read is 100% fact. It is nice however to get several different opinions and come up with a reasonably accurate conclusion. I also realize nothing will replace hands on experience, but I'm just simply taking my sweet time enjoying the game planning phase I'm in at the moment. As I've mentioned in some of my post, the car is a lot of fun to drive in it's current state. What bothers me the most is on the freeway at 70 mph it is really working hard, wish I had a tachometer! Obviously smarter to hit the track, but I love to fly down the freeway at ticket speeds when it's not rush hour lol! It's like therapy for me and it always has been when I'm in a Mopar. I've gathered the 904 with the right parts would be just fine for the 450-500hp I'm shooting for, I just want some top end without beating the hell out of the engine, and came across the whole overdrive idea thinking I could have the best of all worlds. I was just noticing yesterday while reading and researching exactly what you're saying about the price difference or lack thereof between the Dana 60 and the 8.75 differentials! You're right again LOL! I've read a lot of guys also mentioning that the Dana 60 is too heavy for my little 71 Dart Swinger. I'm not worried about shaving seconds off my quarter mile time, I just want to build it right and build it once.If it costs more and takes longer, I'm okay with that. Thanks for your time!
I know I get pretty active on here but please don't let it mislead you into believing that I'm anything more than an adventure hobbyist. Basically just learning as I go along and maybe just a little bit better of the budget to allow me to make more mistakes. But I can tell you the car I have now came with a 7 and a quarter that I never ran because I already had four speed aspirations. I started off with a 8 and 1/4 that never broke with 355 gears in it but after I put a stroker motor in it I figured that was it. I sold it while I was still in good repair. And built that eight and three-quarter for over $1,200. And blew that up as I said within 20 passes. And I was right at about $1,200 with this Dana 60. I can personally attached that once the housings are all separated and all the axles are out and you just have an eight and three quarter housing with the part that holds the gears and all it's probably only a 20 lb difference at the most. The actual part that you're going to use. And mind you that way is right over your back tires where it's needed for traction anyways. I also forgot to mention that $160 Dana that I started with I was able to sell all of the brakes and axles for the truck stuff for $40 so it only ended up costing me a hundred and twenty. And I'm just saying this because you said bulletproof and doing it once the first time not 4 times like I did. If you don't mind that I don't go back and correct my voice command for the few things that I said wrong there I'll continue? If you like freeway driving with a tad of snappiness I would say 3:23's. A big Cam that makes vacuum. Refresh cheap home job rebuild on that transmission. That's probably the easiest part. once you tackle that easy Boogeyman it's all downhill...