According to Zaloga's books on amtracs, the flamethrower version of the LVT(A)-4 was developed but didn't see active service. The only flame-throwing version that saw service was a modified LVT-4 troop carrier with the flamethrower behind an improvised shield.
If you're looking for options, later versions of the LVT(A)-1 and LVT(A)-4 had a ball-mounted .30 cal in the hull, and later LVT(A)-4s had a modified turret with 2 shielded .30 cals instead of the ring-mounted .50 cal. These were known unofficially as the 'Marianas Model'.