I am currently doing a RB swap into my '72 240z, i am using a RB30DET (RB25DE head on the RB30E bottem end)
Once you know the little tricks and what parts to use etc it is a fairly straight forward swap (don't read cheap)
I am spending my money on good bolt on stuff, but i guess you dont have to.
Costings on parts collected so far, in NZ$
RB30 engine (cheap as chips in NewZealand) $150
modified RB25DE (R33 VVT) head with gaskets
& RBDEoil pump etc $900
Custom inlet plenum $1,250
R33 RB25DET 5 speed box $2,000
Billet alloy 80mm thottle body $500
Custom engine mounts $170
Z200r Rb20de rear sump pan & pickup $480
600x300x100 intercooler $500
Parts still needed
Custom rear gbox mount $200?
exhaust manifold $700?
GT35R or similar turbo $2,000?
New stand alone ECU $1500?
Remote wastegate $750?
Pipe work $500?
Fuel rail & injectors $1,000
Random stuff i forgot $2,000
Not trying to scare you here, but this is what this stuff costs, with the right bits it will all bolt in & with my combo above will make in excess of 600hp no drama. I guess it could be done cheaper as i am putting in some good bits.
Ie you could run factory thottle body, inlet plenum, smaller factory type intercooler, cheaper turbo etc and save some dollars. But hey you dont go to all this trouble to get "just a little more power" than an L series do ya?
From a physical size point of view the RB swap would be heaps easier i'm sure than the VG30DETT.
Hope this has been of some help. Get into it!