Looking for advice on a '71 Demon

I would ask the seller if he put a V8 k-frame in it and from what year. Like said above, you can make modifications to a slant frame and it will work. 340/360 cars have stronger torsion bars and usually disc brakes. The spool mount k-frame from later years is the better frame. 71's had a different set up- biscuit style mounts. You can look at pics on Shumacher's web site to see what's involved in a slant to V-8 swap