Street 340 heads/cam recommendation?

any head, indeed. i would personally stick with a head that has shaft mounted rockers. Just my opinion. also the 300 series casting numbers are prone to crack. they are thin. the thermoquad was never offered in a 750. they are 800 and 850. there were some rare ones that were rated at 1000. run the 850 if you can find one. because of their design the engine will handle it just fine. a mild camshaft a stepor two above the 340 camshaft will get the job done and be very reliable.