There are many different opinions on ignition upgrades. Some will say there's no way it can improve your performance over a tuned up stock system, other will swear they experienced significant improvement. sort of like the Throttle body spacer debate.

Here is a writeup on HEI ignition adapted to a 258 with links to a bunch of other write ups on HEI.
HEI on a 258

The writer has done HEI and TFI conversions and says TFI is better (another widely believed opinion). Here is his TFI write up.
TFI on a 258

I did the latter "upgrade", sans new advance springs, just for fun. At the time I had a damaged head on (bent valves and worn guids) and it seemed to help a little. I suspect Sunder is right and on most 258s there will not be any improvement over a properly functioning, well maintained stock system. The "Improvements" many people report could, in many cases, be explained by the fact that their stock system was not up to snuff. In other words, they needed a tuneup. I have since repaired my engine and I'm still using the TFI coil with the Ford 300ci dist cap and wires. The Jeep runs great. I'm sure it would run great with the stock coil, cap and wires but see no need to experiment now. Either conversion will work just fine with a MC 2100 carb. The MC2100 was one of the best things I did for my engines performance on and off road, but I converted from a POS holley. It is a simple carb and I haven't had to mess with it at all since putting it on about three years ago. <img src="/forums/images/graemlins/cheers.gif" alt="" />