"oh, yes lets start with the bars because I don't know anything else and am not smart enough to think about the project in terms of anything but style". <-----this is me imitating you.
Let's start at the beginning:
you bought a 1978 cb400T hawk. Single handledly the most boring motorcycle on the planet. probably because it was cheap (only you don't know that comparativley speaking it really wasn't cheap - if you pay 1 cent for something worthless you are still overpaying). But little you can do about that now - you own it. sucks to be you.
But let's look at this project from a logical standpoint: why do you want a "cafe" bike? is it to get blow jobs from hipster girls? cuz let me tell you girls who give blow jobs bcause you own a motorcycle won't blow you because you own a honda. Is it cuz you want to look cool int he parking lot of that trendy burger joint/independant bookstore/coffee house where the cute grad school girls hang out? cuz if you are decent at paint and fab (I i doubt you are at either) that is about all that bike is good for.
And let's talk about your approach for a minute - clubman bars. The herpes of handlebars. They aren't good looking, they don't give your bike any "street cred" all they do is feed your head about how cool you think you look and maybe, if you don't fuck up the install the first time, some small satisfaction that you are "working" on your bike - all why telegraphing to the world of motorcycling that you actually know nothing.
here is a better approach:
1) does the bike run? if the answer is yes then congrats, you are not half as retarded as most of the newbies out there. If the answer is no then give your self a punch in the nuts because you fucking should have known better.
2) does the bike run well? can you tell if it runs well? If the answer is no - well get figuring this out in a hurry. forget bars, and dress up items. a bike is worthless if it can't get down the street under its own power.
3) did it come with a title? if yes then good boy, you are ahead of the game. If no, punch your self in the dick again for being a tard and once more for talking about clubman bars before you can actually prove you own your bike in a court of law.
4) Ok, if you somehow managed to grope your way through the newbie pitfalls and ended up with a clean bike that runs and has title - take a long hard look at it and ask yourself - if I were a smarter person than I actually am what should I do to this bike to increase my riding pleasure. The answer is not gay as fuck clubman bars. IT is: "maybe I should replace the worn out almost 40 yer old suspension with some modern components and real upgrades", or "is there anything on this bike that doesn't work that should", or "you know, those tires/cables/service items are unknown to me - maybe I should check them out and make sure they are ok", or "those brakes really don't cut it, a grandma in a honda civic can out stop me, maybe I should look for an upgrade. Get the point?
5) you need to stop thinking about bikes as a collection of individual parts and start seeing them as a series of systems. The bars/seat/pegs are all one system connected by the rider - and thus should be changed in unison to fit your particualr needs. Just throwing a set of clubmans on the thing isn't going to cut it because all you will end up with is wrist pain and backache. and no you won't look cool - you'll look like a dork on a honda who is doing his best impression of a dog dragging his ass on the carpet after he has taken an extra gooey shit. The suspension is another system (front and rear) because changing one radically affects the other.
6) plan the bike. sit down, figure out where you want to be, and then make a plan. figure out the small tasks as well as the big ones - that way when it comes time to actually work on your shit you aren't wasting money and time. Need new cables? well if you have already figured out your bar height then you can go ahead and buy a new bar, seat, pegs, and the cables to match. work smarter not harder.
all this could have been avoided with a proper introduction where you post a pic of your bike and actually tell us a little bit about your self. Since you gave so little we were left to assume you are just another TV watching, bandwagon jumping, hipster asshole. If I am wrong - then prove me wrong, give a real introduction.