There is a possibility that you are looking at a 409 instead of a 348. Print out the following info and take it with you to inspect the motor. Even if it turns out to be a 348, it's a score at the money you mentioned.
http://www.show-cars.com/numbers1.htm
You should also know that the Mark IV crankshafts (3.76", 4.00") have the same spacing as the 348/409 cranks. By cutting the main journal diameter from 2.750" to 2.500", the crank will theoretically drop into the block. All W and Mark IV motors use the same 2.200" rod journal size and same 6.135" rod length. So, a guy might be able to drop a 454 crank in (I have no idea of the grinding involved on the block to clear the crank) and make a W-427 (4.125" X 4.000"). Or use a 396/402/427 crank and make a W-402 (4.125" X 3.760").
Probably the biggest cost in doing this would be the pistons, which would probably have to be custom made unless another member of this board knows the whereabouts of some special pistons on a shelf somewhere. .