Snakesource,
I decided to go with the signaw conversion do to my experience with signaw. You can more than likely locate a signaw box cheaper than a toy box as well. Go to
www.car-part.com and look up a 67-68 impala - I bought mine and had it shipped for $45.00 and in good shape. If you are interested in the signaw you need to buy the kits or have some parts made yourself. I had some plate cut for my box and just cut the inside part of the frame out so I can weld the new plate in. If you are interested e-mail me tomorrow and I'll forward you the design on the plate. They have a plate design in the tech part of the site but it doesn't print correctly.
Let me know if I can gine you more info.