On the weight issue, I have to say that we disagree. My Miradas (318s) are at 3500# (1980 J bodies are even lighter due to the use of aluminum bumper bars). They are loaded to the gills, and are also on the longer 112" wheelbase of the 4 door M body. The F body coupe is on a 108" wheelbase, and is overall both shorter and smaller, it is very easiiy in the 3200# range for a small block V8. The "heavy K frame" of the F, M, and J is due to the suspension design. The K frame itself may be heavier, but the B body is heavier in other places of the frame. This is really closer to a push in that regard. The A body of 1969 has a curb weight of 2888 with a slant 6.
As for time slips, etc. you would be comparing apples and oranges, in a number of ways. Firstly, the '69 Road Runner has a higher compression ratio, which helps both hp and torque. Secondly, argument can be made that the B body Road Runner times are slow due to lack of traction, which would be a really fair assessment, considering both the size and composition of tires in the late 1960s; for the most part, a lot of time was lost spinning tires. However, I will say this: give me an F body Road Runner with a 360 Magnum, Engine Quest heads (out of the boxm no porting), decent exhaust system, and a carb and ignition system that is properly tuned for that car , and I will take on a stock 1969 Road Rnner with a 383, and I have a better than even chance of seeing the end of the drag strip first.
Also, while of interest, 1/4 mile times really don't have anything to do with anything useful. While a gauge of engine power, that is all they are good for. They do nothing with regards to fun to drive factor, day in day out usability, cornering, or any of the other things that we need out of our cars. There is also the issues of tuned cars being sent by the manufacturer, driver ability, track condition, etc., to make any 1/4 mile comparison pretty meaningless.
My issue is not with the B body Road Runner, but rather with the idiot in the video who dismissed the F body Road Runner as a "trim package" for the Volare. As most here will know, the F body Road Runner does have a lot of components to it that came from the police and HD parts books, making it much more than "just a trim package". The video dissed the F body Road Runner out of ignorance, pure and simple, in order to furher raise the reputation of the original B body. They didn't have to do that; the reputation of the original is well established, and is unassailable. It does however, show the "rose colored glasses" nature of the experts on this, and many other episodes. It is great to remember the muscle cars of the late 1960s, and respect them for what they were. However, to hold those cars in high regard as some benchmark of high performance would be truly ignorant. I have nothing but the outmost respect for the original Hemi, yet I also recognize that a Hellcat Challenger will leave any late 1960s/early 1970s Hemi car like it was parked. I think LS7 or even ZL1 Corvettes are really cool, real "he-man's" cars, but all of that doesn't change the fact that today's Z06 Corvette will render it a small dot in its rear view mirror pretty quick. Same applies in both cases to 0-60 times, 1/4 mile times, or any other peformance measure. I respect those cars as being great cars FOR THEIR DAY. We are not in those days, we here today, and in today's day and age, they are slow, don't stop, and don't get around corners very well. They are, beyond any shadow of a doubt, cool. They look great, But they are not, in my opinion worth the kind of money people are putting out for them, nor, by today's standards, aside from looks or cool factor, are they very good cars overall.
BTW, I don't have any bias towards or against the F body. I don't own one; I own 3 J bodies. I just took exception to the way the "expert" on this video just dismissed the F body Road Runner as a trim package. Did you know that the F Body 360 Road Runner, in 1977, was as fast as a Z-28 or L82 Corvette? No, it was not as fast as a big block Road Runner, but it was about as fast as any other factory car. And, today, if you want to build an F body Road Runner to be as fast as a stock 383 Road Runner, you could do it for about $3-4K, You can build an F body to go pretty much as fast as you can stand, except you don't have to pay $50K for the car itself.
None of the F, M, or J cars came with a big block from the factory, true. Have you ever asked yourself, however, why is it so easy to get a big block into these cars? Ever wonder why, even though Chrysler did a complete re-design of the K member when the F bodies came out, why there was still room for a big block, even though they could have designed it so the big block wouldn't fit. There are lots of articles on how to get big blocks into J bodies, and aside from brake booster interference issues, it is a pretty good fit, even with power steering, air conditioning and power brakes hooked up. With the lighter weight of the cars, that famous big block kick will be just that much more satisfying.