Gassing up camrys

TOYOTA, like all carmakers, won't recommend modifying their cars in any way and that includes converting them to LPG. They spent millions of dollars developing cars to set specifications and know nothing of the consequences of modifying them. So they always say not to modify. Probably the only problem you will face is the valve recession you mention. Talk to a respected specialist and ask their advice. The difficulty with cars like the Camry is the LPG conversion industry has little experience with them.