I'm assuming that your74 cb350 is an F bike (4 cyl) and not a twin. I am 90% sure the cb350 twin drum front ends are a direct swap to the later cb350Fs (and the twins). Since you are doing it for looks and not that concerned with actual braking power (or else you would keep the disc) the stock cb350 drum should be good for most street riding.
When talking about heavier bikes (like the 350/400/550/750 fours) there is far and away advantages to running discs. Those bikes are heavy and any weight savings is a blessing, espically reciprocating weight so discs have the advantage right off the bat. But more importantly drum brakes heat up quicker and retain heat longer than a disc setup and on bikes like the 750 would burn through brake shoes faster than a disc with a drilled rotor. For the Kettle (Gt750) suzuki used a 4ls front brake because the bike weighted in excess of 500 lbs and previous expirements with drums brakes showed them to be inadiquate in fade, longevity, and overall stopping power. Now a 350 four isn't going to wear out drums like a big old 750 but why peanlize yourself with the weight.
Unless you need a drum brake for a racing class, leave the drum at home. By the 1970s most race bikes ran disc or dual disc drilled front brakes which can look just as cool as a drum when executed properly (like with a set of lesters and a polished airheart caliper).
