I can't believe nobody has mentioned that an OEM 400 crank will not fit in a 1 piece rear main seal block. The OP stated he just wanted to put a 400 crank in...All GMT400s came from the factory with a 1 piece rear main seal block. All 400 sbc motors are 2 piece rear main seal. The crankshaft will not interchange between the two.
That said, you can run an aftermarket crank and do a little clearancing to make the longer stroke work. I would strongly suggest talking to a machine shop first. More than likely they have done a 383 sbc before and will know exactly what they need to do.
There are plenty of stroker kits available, and this is probably the best 'budget-wise" to create a 383 in a TBI or Vortec block. Actually your best bet is a Vortec block since it has the provisions for a roller cam already. The Vortec heads are also great heads for a budget 383 build. The weak link will be the TBI or the Vortec based EFI. A carb or aftermarket EFI would be best to take advantage of the extra cubic inches. However with a mild cam and stock EFI setup, I would think it should make alot of torque.
Also keep in mind Vortec heads need the valvespring pads machined if going to an aftermarket cam. You cannot put aftermarket valvesprings on a stock Vortec head without some machine work.
EDIT - I see the OP has a Vortec already (I assume the 1998 truck). If upgrading to e 383 ci under the Vortec Injection/Ignition, you will most certainly need a proper tune when done. Figure on $300-$500 for a proper dyno tune or you could try some of the mail order tunes. I personally would rather put my vehicle on a dyno than rely on a mail order tune.