Although the I made the above statements I will add this.

I have modified plenty of guns. If the ops buys a gun its his and he should feel free to do as he wishes. It would actually be easier to make a 6 inch in to a 3 1/2 than a 4". Reason is on the 6" you could salvage the front sight ramp easier. The roll mark. Take a small round face hamer and tap the roll mark area a lot. This will move metal into the low areas. Then you could make a wood or aluminum piece that matched the curve of the side of the barrel, back iit with sand paper and sand of the marks. Labor of love. Ernie at Ble Lightning Stencil could make you a couple stencils and with those and a small 12 volt batttery charge you could apply pretty could fake roll marks. Now you have a 3 1/2: N frame 357, but far from a 3 1/2 327.
Hey I hade a 1917 into a 3 1/2" barreled 45acp by cutting down a 1950 barrel and milling the frame for adjustable sights. It is a handy gun, especially since I cut down the grip frame. I would post a picture, but out of town with out flash drive with most of my gun pics and the one here under 1917 Combat
Has that stupid photo bucket deal on it