What is the floor plate for anyway?
A good video, FYI, the first example would be extremely rare.
http://www.youtube.com/watch?v=wxb8LR5bMUM
Your 78 is an ADL version.
Your best bet for a replacement stock is to look for a factory takeoff on ebay or one some place like gunbroker, the classified on this and other gun related forums. Folks often buy a high end aftermarket stock and sell brand new takeoffs dirt cheap. I've seen synthetics sell for $35 and walnut for around
$100. There are very, very few ADL options for after market stocks other than high end $500+ stocks
It would not be worth the expense to convert to BDL. The parts alone, not counting the stock would cost more than your rifle is worth.
Your ADL design has several advantages, and all things considered I would just as soon have my rifles that way. It reduces cost and weight. Since there is no cutout in the stock for the floorplate, the stock is stiffer, and theoretically more accurate. While rare, floorplates have been known to open and dump your ammo on the ground. Many dangerous game guides weld theirs shut just to eliminate that possibility.