I've had one built recently for my long distance rally 144 (=heavy with all the needed extras) with the good bits coming from Tinus Tuning in Holland. As B20Paul said, you do need to do the complete package. I've just done a 7 day special stage rally in central Australia - nasty dirt, dry sandy river crossings, rocks, you name it. Not much more top end, but the increase in midrange torque made it all worth while.

We built the engine to 9:1 specifically for another long rally next year but if you put in more compression and a more aggressive cam, it would be spectacular in the lighter 120.

As for cost, compared with offset grinding a 40+ year old crank, you get a new billet crank and all the associated bits for not a huge amount more. The real expense comes in getting the head done and the engine put together properly, unless you do that yourself.
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JohnH, Sydney, Australia