What we have here is a rather nice Postwar conversion of a Canadian HSDR to a HSAT.
There is very little published information out there concerning this type of conversion and most of that can be found is in the book by Roger Lucy Tin Lids In the late 1940's and early 1950's as Canada began to rebuild her Airborne forces and the Mobile Strike Force. They had enough British AB helmets for the PPCLI, but the RCR and R22R did not have helmets.There was an extreme shortage of Mk II Airborne helmets and needing to out fit two other Army groups the decision was made to convert existing Mk I DR helmets that were in military stores to meet the expanding need.
The HSDR's were turned 180° so the brow pad became a neck support the skirting was cut off ,dome pads were some times added as well, the shells were drilled out to accommodate new leather harnesses in the Mk I configuration the requirement had been for 500 of these converted AB helmets but it is possible that they converted some more the exact number is not known.
The helmet body is dated to 1944 and was produced by Canadian Motorlamp Company ( C.L./C. ) and bares there stamp in the interior low on the skirt near the rim .
The liners were manufactured by Backstay Standards ( BS ) and bare there company logo and date and can be found marked with the C-Broad arrow Canadian government acceptance stamp on the reverse of the sweat band and in the helmet body .
This example was originally sporting three British wartime produced camo nets applied to the exterior of the shell when found but at time of resale was only offered with one example as part of the deal with the seller .
The rim has been wrapped with a strip of rubber this could have been applied to protect the rim and or to tuck the nets under to help keep them better secured as well as having a strip of inner tube applied half way down the shell to help keep the nets in place.
As to the leather harness it has been speculated that they were either WW II British surplus and or post war Canadian produced this particular harness is the Canadian produced variation.
IMO the harness looks to be well used as is evident in the chin cup and adjacent pull strap and the copper and brass bolts,fittings and rivets are starting to show the signs of green verdigris which tells me that the harness has some genuine age to it .