For a start- saws do not have blades- they have bars.
So it came without bar and chain?
First thing to check is the sprocket or spur that drives the chain off of the clutch- that will tell you if it is still set up for 3/8 chain or is someone has swapped it on to .325.
IF it is still 3/8 and you wish to retain factory fit- then yes you are correct, 20 inch bar and a chain of 72 drive links- BUT the mount for this saw is K095 or HSM- NOT D009 or HLM.
Driver, bar nose sprocket and chain pitch must all match up- chain and the gap between the rails (gauge) must match up, bar mount must match the studs and bar pad of the saw- so the oil delivery hole, adjuster hole lines up and the fit is not sloppy on the studs.
Decide your gauge choice on what is best available to you locally- usually 0.050 or 0.063- Worldwide Husqvarna standard is 0.058 gauge but that is not a common size in the US of A.