/6-225 to 318 Scamp conversion

Your problems are absolutely two fold and possibly three..
First the transmission. A slant 6 transmission will not fit on a V8. And slant 6's never did come with a 727. They came with a 904. If they were automatic. So the first thing you got to do is shot for a transmission. I would recommend a small block 904 transmission.
Working our way forward second would be the motor mounts. the V8 will not Mount where the slant six mounted unless you either have a motor mount conversion kit or a V8 k frame. And then you would need the motor mounts for the V8 as well.
Putting a magnum v8 and is a great idea. Although there are many things from top to bottom and front to back that must be taken into consideration. The easiest way is to yes go to Speedmaster and get a $226 4 barrel intake manifold. Maybe wait till Black Friday and get it cheaper. Four-barrel carburetor. You'll need to go to I can't remember the place but they sell a piece that goes on the end of the cam to run your fuel pump. as it doesn't have it because Magnums have fuel injection. You'll need a distributor and the electrical system from an LA motor and you'll need everything from the timing chain cover forward. And you'll need a car oil pan and pick up tube as you're putting it in a car and the one on the original Magnum engine is from a truck.
I could be wrong about some stuff as I haven't done the swap but I've looked into it quite a bit. I'm sure others will chime in with what I got wrong and what I forgot or don't know...