Yes the V.Z. 24, Some alittle rough but all strong. Good action and as you have probably discovered quite inexpensive. Some 98 actions are not the best to work with, you want one from a good manufacture such as F.N. Bruno, C.Z. and others. The V.Z. 24 falls into this class and if clean is a good start for a custom rifle.
Though some people open the standard 98 up to take .375 length cartridges it is not a good practice from the liability aspect as the action is weakened. There is a way to do this without weakining it but we can discus that another time. 3006 length is not a problem at all but there two length magazines and the shorter one has to be opened up a bit. So always check your feeding before you blue the beast.
35 whelen, and the .338-06 are good cartridges, if you like something different check out 9.3X62 and the .358 Norma mag. Yes if you open up the bolt face and the rails of the action standard length magnums up to the .458 Winchester are not a problem. I do not know what you are going to do about the bolt handle but if you are going to forge it down while you are at it you can stretck it about a quarter of an inch and reshape the knob, this gives a much better appearence. One other thing check out the Kiplinger single set trigger for these actions.
Hope I have been of some help.

Your Friend
Jud