71 scamp build, need direction

Pretty ambitious. I suggest you do a lot of reading first. Many posts here on disk brake conversions, BBP changes, and wheels. You can now get nice 17" SBP wheels fairly affordable (see posts), which would clear any disk brakes. People claim it is simple to change to BBP front and change the rear, cut the driveshaft, ..., but they have much experience and you sound like a newbie. Don't start something that will leave your frustrated and stranded. You can get front disk kits that bolt up to your existing drum spindles.

Re engine, what does "mildly fast" mean? The 225 can be great for low-end torque, like leaving a stop sign sharply, which is what most people notice when driving. High horsepower comes from an engine screaming at 5000 rpm. You would look like an idiot driving around like that in 1st gear, so don't fixate on horsepower. That is why most V-8's came with 2 bbl carburetors.