If this has been covered b4, forgive me. I am looking at a 340-ish cam for my '74 318/904 challenger. I say "ish" because I'm looking at two of Lunati's 273-360 Mopar cams:
268/276, .494/.513 lift or
256/262, .454/.475 lift
OR
the stock 340; p/n 2899206 268/276,.430/.444 lift.
My question is: Will I need new valve springs with any or all of these cams? BTW, any opinions on which cam to pick for overall drive-ability vs performance? I won't be racing it on the strip but I want to be fun while still be something my wife can drive once or twice (OK, once! LOL)

The stock springs are pretty whimpy when it comes to performance. While with the smaller cam you more than likely wouldn't have a coil bind problem you would not have near the spring pressures recommended. The bigger cam for sure no way. You will have coil bind for sure.

If the engine is fairly stock use the smaller cam.A NEW set of springs is mandatory.The factory performance 340 springs will handle it (smaller one) but use the recommended Lunati spring.

250 260 ish @ .050 are big cams!! need roller springs!!

might be what you need when people qote advertised duration which means almost nothing than the @ .050 or at least the PN and a link to it somewhere!!
Roller springs are the ones on your lawn roller.

I can find the specs for the MP cam but the PN's don't match?

FYI..

with any SB lunati cam you can use the comp 901-16 springs

all the lunati SB cams use the same lunati spring across the board

901-16 springs drop on with stock retainers and seals with no machine work and can be done with out r&r the heads

the lunati springs are a double with a damper and need seals and machine work to use them

I went this way when going to the lunati 60710 voodoo roller cam in my 318 after I got the cam and springs from lunati...then got the comps springs

they are within 10 lbs of each other,I have been to 6200 rpms with it with no valve float,all though the cam noses over after 5500rpm

just had to try to see if they would float but they are good to go

I would use the comp 901-16 with the mopar cam also,IMHO

they are good up to the .500 lift range

I have a 360 with the lunati bracket master 292/292 cam with the comp 901-16 also

way cheaper..comps are around the 79$ mark and the lunatis are around the 130$ mark...of couse results vary with the speed shop prices

good luck