I hope you don't mind me hoping in on your thread but I'm going through a similar dilemma.
I have a fully working l24/e88 combo. A disassembled f54/n47 (flattop)combo which needs a new cam (smoothed intake), and the bottom end rebuilt.
There is also a L28et in the junkyard, that has been sitting there for two years. Apparently turns of freely. A turbo swap would be fun in the future.
A) rebuild the bottom of my f54, get a cam kit from rebello and call it a day
buy turbo motor, re-ring it and toss it in NA
C) put flattops into turbo block and run p90 head
Options B/C I would probably put in valvetrain from working l24 motor.
All the options cost money. What to do, what to do.