I think the hydraulic vs mechanical cams are different (the journal supports are different diameters...?) so they aren't cross compatible AFAIK. There are pros and cons with both valvetrain set ups. Mechanical requires adjustments from time to time but offer full lift once set (better from a performance viewpoint), hydraulics don't need manual adjustment but do wear out and lose lift when engine oil is overdue for changing or there's an oil pressure issue. Also the lubrication in the mechanical heads is a bit 'hit and miss' (I know this is an issue with mechanical G63B heads but IDK about the 4G54).