welcome to the shop Gary, don't forgit to get some pictures to the editor for the gallery, and link us up to some, we love pictures here
the stock 59 motor would be a 235, and the later 250 will have a different mounting arrangement, and no doubt different exhaust configuration, but if the price is right, anything could be made to work .... haven't heard of anyone here doing just that switch, but maybe .... also don't know if the bellhousing would mate to the stock 4speed
you might also consider going to a small block, as the 283 was an option then, and might be an easier switch
Bill
