68 dart with running 383 auto - advice to build another motor

Hello,
Father son project in the works. This is a running driving car now 383, 3000 stall so we are told, 391 rear gears mini tubbed. I know this is a loaded question with lots of directions but could we gather parts to build something around a 509 purple shaft cam or wilder idle on pump gas no concerns about vacuum we are manual disc breaks but on a budget? Piston choices seem to be limited without spending $1000.00 bucks alone on them. I assume with a big cam we will need notched pistons for valve clearance.
My son is 19 so I don't think we need a stroker build yet for him. I would rather work his way up in power levels but we both like a nasty idle. He has already bent a few push rods ha ha in the 383.

What I have is a 400 bare block and crank 73 ish
a 67 ish 383 block and crank
No pistons or rods for either.

Locally I have 452 or 906 heads for sale and possibly some closed chamber heads.
There are also a few 383 and 440's around.
Also a 361 1965 complete motor cheap- maybe take this for rods and crank for a 383 /400 build?

Looking for a recipe of major parts, compression and zero deck etc...
Build another motor on the side so we can keep driving.

thanks Greg