A complete stroker rotating assembly will cost you right about $2K. A set of ported iron heads will be another $1100 - $1400 depending on what you go with. Going that route and staying within your $4K budget will mean doing the assembly and installation work yourself as you will still have to pay for the block machine work and miscellaneous parts such as gaskets, oil pump, cam & lifters, etc. etc.
I would not count on PAW to be able to give you any meaningful technical advice concerning blocks & heads. They just sell parts, mostly for Chevies and Fords.
Consulting a Pontiac expert is a good idea. If you can fit the stroker kit into your budget, it's a great way to go for a heavy, mild geared car such as yours. Big cubes = big torque which is what you'll need. Build a big, mild-mannered engine and you'll have a huge, comfortable car that can dust off most ricers without breaking a sweat.
----------------------------
'72 Formula 400 Lucerne Blue, Blue Deluxe interior - My first car!
'73 Firebird 400/4-speed Black on Black, mix & match.