I just took a look at that 58 your considering I like it!
if I was fixing it up I'd either take apart the 430 just to inspect and freshen it up with new rings, bearings and gaskets, polish the crank, replace the oil pump, have the rods rebuilt with arp bolts for cheap insurance against fatigued bolts and maybe put in a new cam and get the heads freshened up....
or if I was going to modify it from original, I'd drop in a 460 or a v10.
Sequential port MAF injection for a 460 is rare, but instead of shelling out a few grand for a california only 460 maf injection setup...people are using or upping their injectors on the speed density manifolds, adding an aftermarket maf and using a mustang computer (ho i think) to run sequential port injection on the 460.