Depends entirely on you. Tuneup and supercharger drive ratio will determine how long the engine lasts.
I'd use the '73 engine, 7.2:1 stock compression and all.
The heads on that engine, if they're not the industrial heads with exhaust manifold bolts not in a straight line, will be 213s. They'll have an induction hardened valve seat for at least the exhaust valve, I sort of remember my 213s having the heat rings around both seats after hot-tanking. They may or may not use "peanut" plugs, mine used a regular 3/8" reach gasketed seat plug, some have the tapered seat 5/8" socket plug.
There's nothing magic about 906s. I'd spend the time bowl porting the 213s. I'd use a cam with around 240 degrees at 50 lift.
An 8-71 on a 440 you will want maybe a 1:1 drive ratio or less to avoid overboosting. Make sure you start out with a super rich mixture and 32 degrees total advance at 3000 rpm.

If you keep manifold pressure below 5psi gauge I don't think yor bottom end will grenade. And as far as a '73 block or forged crank, nothing wrong with it at all, it's not a throwaway. I don't know where you got that idea.
R.