The 250 x flow are a really good cheap donk,especially the xd,xe,xf era
Free to a coupla hundred will get ya a complete running falcon
They looove the juice,always have
Comparing the engine cost Vs conversion cost ,6 cyl against V8
V8 would be the better option
Compring a 4.1 L petrol against an SD33T,well would ceratinly be a good little test
Money is on the SD
Comparing the L28 petrol against the x flow well thats different
Really depends what sorta vintage x flow your chasin,pre EFI,post EFI ect ect
Comparing say and old school x flow against an old school hemi 6,the hemi will absolutely smash the x flow
Then again so will the wallet cope a hiding running the hemi
The new later model falcon motors are the go