Some builders (e.g.http://home.alltel.net/franklinframe/) charge only $75 to braze in a new steerer tube, including materials. They have to drill out any pins / nails, de-braze the old tube, and braze in a new one, in an alignment jig.
If you consider that a 531 fork typically costs $50 on ebay if you find the right type with a short tube, you end up paying a total of $125 for a fork, ( paint will be extra ). This is a relative bargain compared to a $300 fork made from scratch that may not have any paint, and may not have any chrome.
With the proper long steerer tube, you can often use a correct headset or whatever headset you want, which can also save $$$ (no need for a campy track headset), or reduce anguish over the quality of your restoration, etc.
- Don Gillies San Diego, CA, USA
P.S. for the particular case of a masi, it will be extra $$$ to dechrome the fork crown and rechrome it later. But, there's nothing more satisfying in bicycle repair, imho, than doing things right ..