yes you can drop a rb26 in a r33. Stock MkIV turbo supra are a lot faster then a r33 GTSt.
Supra are pretty heavy, so you need a lot of HP to get them going. 800hp from a Supra is about the same as 500hp from a silvia. (performance wise)
Between the 2 motors, 2jz and Rb26. The Rb26 will cost u more, but you will get better hp.