Both...I think the idea of a rebuilding the block is historical importance for me. Obviously it may not be salvageable, or may not be worth salvaging and then a similar bolt-in replacement would be the next option. In addition, given the transmission and other issues inside the engine bay, going to a modern V6 has a lot of additional things. Front cross memeber and motor mounts often have to be redone/moved, my old ross steering doesn't work with many modern exhaust systems (although the ross is pretty much junk, but add a saginaw swap to the list), and the T14 transmission is a bit unique as well and also has to be compatible with the D18 and Warn OD. Its truly a challenge of change one thing and the chain reaction of mods gets big. Changing to a modern transmission and TC eliminates use of a D18 (or adapter needed). I can only use a D18 TC as I have an offset rear differential. and any increases in transmission and tc lengths such as adapters causes an already short driveshaft to become even shorter. Not saying it can't be done (heck its been done a lot)...just that I don't think I want to go down that road.
The howell TBI for the 225 is relatively new. $1400 is the standard cost whether from howell, EZ EFI, Powerjection or custom stuff from Hamilton FI. A few on the earlycj5 forum have been checking out the holley. The general consensus has been EZ EFI is the best way to go with least amount of hassle. Powerjection can work really well, but takes a lot of tuning effort. Some these (maybe the howell?) require a different intake manifold (like an Offy dual plane). There is always an issue with an odd fire engine and the computers. The EZ EFI is probably the best one for it because its easiest to separate the fuel control from the ignition (and let the traditional distributor with pertronix, mechanical advance and vacuum advance control the spark - or go hei). The last problem with TBI is figuring out fuel delivery - my OEM style vented tanks without baffles can cause some problems, as well as routing fuel line to handle the exra pressure - not ridiculously difficult, but not necessarily trivial either. I like my dual tank set-up right now, but uncertain what would need to be done to make it TBI compatible.
Lots to think about...