I am currently exploring this upgrade myself and this is what I've learned.
Although the SBK forks you're getting are cheap, you will need to figure in the cost of a triple clamp and new clip-ons, $400-500.
You also have an option to have your existing forks upgraded with Racetech or LE hardware, they will beat stock SBK forks, performance-wise, even if non-adjustable. Labor and parts will cost less than your SBK set-up.
Both upgrading and replacing are valid options. Just be sure the cheap forks are not the older type with 40mm caliper mounts, in which case you'll be paying $150 for conversion brackets, plus if they're old, they may require servicing, at a price. An easy way to spot an old 40mm fork is the straight caliper mount, vs. the newer 65mm curved one, the latter also has the red Showa logo on the bottom.
Other people who upgraded usually become interested in upgrading the remaining stock suspension.
Engine size makes no difference about the utility of good suspension and you can always take them with you to a bigger bike.
Nope, the caliper mounting bosses are part of the fork lower.
BTW, I'd say that it's debatable whether or not a Race Tech'd (or similar) non-adjustable Marzocchi fork is going to be better than an off-the-shelf SBK Showa. That just depends on how well the springs, oil, and valving in the SBK fork fit the rider's weight and riding style. Of course, if you're an advanced or track rider, a professionally set-up SBK fork is going to put you way ahead of anything that you can do with the Marzocchi.
The advantage of the SBK forks over the non-adjustable Monster forks is that even without Race Tech (or similar), if you arent too huge or too small, you can at least get the pre-load and damping close to right. For anybody that's over 175 or so and rides even remotely agressively, the damping and springs in the OEM Marzocchis sucks.
Actually, as mentioned above, if you do get the forks right for your weight and style without doing anything with the shock, chances are it'll just amplify any deficiencies with the shock set-up.
I emailed Ducati asking which manufacturer made the forks for the 2002 620 and this is their reply:
"thank you for your message and please apologize the delay of our answer.
Referring to your request we inform you that your M620 Dark has been manufactured with a Marzocchi.
For any further information our official Dealer Network in your country is at your disposal.
Ducati Motor Holding Spa
How's about a little advice? I know I can replace the shock on my 620. But.....what about the forks? Don't want SBK forks; don't want to go to clip-ons. (Wrists are too old!) What are the options? From what I've been following on the list, I'm at the upper weight range for the stock set-up (175-180 lbs). Any suggestions? TIA