There is a version of the later x flow based on the 711M, called the AX made in south africa, it is basically a thicker walled block, that can be taken out easily to 1825cc, with oversize pistons, with stroking around 2000cc is available using a modified datsun crank.
On true x flow 711 blocks 1760cc(pistons only) was regarded as a safe limit, this may be what the advertiser means ?
tabetha