The trick I've found with Marlin 336's is that you need the scope as low as possible because the comb of the stock is low for the use of iron sights. I don't think your 40mm bell will do this. I use Leupold straight tube 20mm scopes on all my scoped Marlins. The best, and lowest combo I've found is using Warne weaver type bases with Burris low zee rings. The super low Burris ring is even better but no longer in production. It's difficult to get a good cheek weld with anything much higher.
Good Luck,
Rick
This right here. I have a 1-4x20 Leupold in super low Burris zee's on my 336.
