If you're looking at rebuilding have you considered buying a blown RB25 & freshening that up?
Might not be as dear as you seem to think. Wiring can be done cheap (can point you in the right direction there if you need), tailshaft can be done cheap, gearbox mount nearly free, may be able to re-use your turbo unless its already running out of puff on the 20?
At least ring around & get some prices & compare that to what you will spend on this 20/22.
Will end up with a slightly later model base engine, more capacity ( torque), VCT, better flowing standard head, etc. In my opinion well worth it if you can....