Aha! This sounds interesting:
No, the flame guns developed for the M4 by the Army were the E4R2-5R1
and E4R3-5R1 (standardized as the M3-4 and M3-3), the E6-R1 and the
E7-7 (two further series were completed postwar). They were all kits
that could be installed in vehicles and then removed. The Marines also
used the POA, which were complete conversions of existing vehciles.
But none of the conversion kits arrived in the ETO in time for
NEPTUNE, the first arrived and were installed in the initial shipment
of M4A3E2 in late September, which is why Crocs of 141 RTR were loaned
to the US for use at Brest. Operating Tanks at Omaha first 6 hours - soc.history.war.world-war-ii | Google Groups
.