Mod S is a 'modification' of the factory S profile. Typically a bit more lift is added. There is also the mod solex and mod 906
...oh wait, the factory did that one...RSR sprint
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Short of tossing in a 3.0, and I do hate that thought, but it is cost effective, do a search on Grady and 2.8S. The 2.8 cylinders are a bit harder to find but are around. Figure $1.2k for replate and hone to fit. 90 mm 2.7 cylinders are more common and wouldn't be far off the mark. Don't bore stock 90s to 92 mm. They get real thin at the CE groove and chip if a detonation even looks crosseyed.
There is nothing wrong with the T crank. It will spin up quick, just keep it to 7.2k rpm.
You will need to chase up some heads. The T heads won't move enough air. The stock 36 mm heads flow really well. The factory did a good job. They will feed a 7.2k limit 2.8/2.9 (70.4 mm crank) or a 8.5k rpm 2.5/2.6 (66 mm), just.
IMHO the best $$$ you can spend is the $400 to get your heads twin plugged. Can't afford the fancy, but awesome looking twin plug distributor just yet? Just put the lower plugs in and put the covers right back on and drive till you can. It will future proof you to gasoline and will make the engine even at stock CRs. Less advance is good for longevity. If your going to EFI, the microsquirt is pre built with surface mount components, has twin plug built in, is darn tiny, weather sealed, and has both sets of trims. Oh yea, it's like $340.
You will spend, it just depends on where
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