It looks like Egge's website has forgotten about the 273, they used to make Commando pistons. But there are plenty of manufacturers that will tool up sets of custom forgings for $1K or less.
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Egges does have Hi-Compression pistons for 273 commandos. I've checked that out. But I decided to choose pistons from AutoTec with rings from Hastings. Real nice quality-pistons for approx. $ 625.-