To get 288 cubic inches from a standard stroke 270 (4" stroke) would require an over bore of 1/8" (0.125") I don't think there's enough cylinder wall thickness to get 298 from the same block. A piston that big gets into the category of extremely expensive custom forged items. Assuming you can find someone to build one that size (Venolia, perhaps?) be prepared to spend upwards of a thousand dollars for six pistons. Then you'll have an engine suitable only for racing. It would be a lot simpler to try to find a GMC 302 engine instead of modifying the 270.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
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