You will note that I am using an insert parting tool blade. Different configuration tips can be used such as round or square end as they can be used for grooving as well as parting off.
These type of blades are set straight and all the appropriate relief angles are built into the tip which only needs be set on center.
I built a holder as the only ones that would hold a 32 mm blade would not go high enough. I used a dovetail cutter in a mill to cut slight angles for a wedge effect as the cover strip is tightened down but a straight cutter,(end mill),in the chuck would do the job.
You have said you are thinking about a Multifix toolpost but have not said what you actually have. There is nothing stopping you modifying whatever is to hand, the only proviso's being as stated above with regard to orientation and being able to obtain the correct center height.
If using HSS then you would need to machine the groove in the tool holder at an suitable angle or grind the blade to provide clearance or both.
There are many advantages or running upside down 1st being the tool will be pushed away from the cut if overloaded 2nd and what I love is all those chips curling and falling out of the cut. Well worth the time to sort out. Hope that helps.