That cutter system is what was known as a Slotted Collar Head (also known as a French Spindle Head) and has been banned over here for a couple of decades. They have a very bad rep' but were really good for handrailing jobs, so long as your hands and digits kept out of the way [wink].
What size spindle arbour is it and can you swap it out for a different arbour, to be able to use limited blocks for safer working (by 'limited' I mean limited in the amount each blade removes per pass, not limited as in can only do few tasks)
Also can you get a power feed to fit on it, keeps fingers out of the way and improves the end result, for most door making tasks it would be a huge assistance. (Negates the need for an assistant on the outfeed end)
If you need any general info on using spindle moulders/shapers let me know as I have used various makes for many projects over the years and have a very good understanding of them, (and all my digits ;D)
Below are a couple of pics of limited cutter blocks and a selection of cutters to fit the CMT block that needs two cutting knives and two limiting (dull) knives. That I own and use.
Rob.
Edit to add info on French Head.