I'd start by checking with your local LEOs to make sure teh frames are not stolen and can be registered after you build it.
If they come up clean, start the research into what works on those bikes and how you want it to look and perform. Since you are not starting with a perfect bike, you can feel free to do whatever you want with them in terms of modification. Carpy built a few cafe racers in the old style and might be a good place to start.
As the plan starts to evolve, you have lots of spares to work with, and by the time you finish there will be lots of parts to sell off and recoup some cash.
Take your time to work up a plan. I use CAD v0.0 (cardboard aided design) so I grab decent pictures off the web of a stock bike without tank and seat and print multiple copies and start playing with shapes and ideas. I also grab pictures of other builds of the bike I'm working on as well as other makes for ideas.
Try not to lock in too hard on one idea up front, but be open to lots of ideas and refine your plan as you go.
One place to start is an F2 tank, CR750 seat, good 4 into 1 exhaust, Dyna ignition, stock carbs, hot cam and big bore pistons with superbike bars and rear set pegs. Decent rubber - BT45 or AM26 on slightly wider rims and a brake upgrade would be a good place to start. Front forks and brakes are weak by modern standards, so I'd look at say early R6 conventional forks and brakes or maybe SV650 or even Katana or CBR600F4 forks ie conventional and long enough to work. Most USD forks are too short and screw up handling.
So you keep the classic look and update handling brakes and engine performance so it does everything better than stock without turning it into a full on race bike that can't be ridden on the street safely or comfortably.
I'm sure you will come up with your own ideas, but take your time to think about it. That's half the fun.