A properly adjusted Moto Guzzi gear selection system should not clunk or slam into gear.(I'm speaking about Big Twins begining with the V7 Sport and newer) I say, gear selection system, because smooth shifts depend on not only a carefully assembled and shimmed gearbox, but also the condition and adjustment of the clutch lever, cable and pushrod actuating arm, the condition of the clutch and all of it's components, the condition of the shift linkage and even the endfloat of the crank. Check my TIPS section for ideas on how to keep your shifts smooth and your gearbox healthy.
Moto Guzzis standard five speed gearbox, which is in the vast majority of the bikes produced in the last 30+ years, is a pretty decent unit which can work quite well for many, many miles. As you may have heard from other sources, it was primarily inconsistant shimming of the layshaft, mainshaft and especially the shift drum by the factory which caused many Moto Guzzis to clunk or slam into gear, right from new.