I was contemplating something similar myself, scratch built. twin opposed spindles.
How well are you setup engineering wise??
You cant get a (bar) blade for an 18" MTD star boss, From the mower joint i bought an adpater that came fitted with swinging blades. If you could make something similar you could go with off the shelf Greenfileds blades.
Now i havent checked but thats provided the LH and RH throw are the same size and shape blade. Actually that wouldnt matter.
The idea behind it was that you can buy them easy and they will be longer and a bit more weighty than a push mower blade therefore whatever you make up to mount them on will be smaller and have less reciprocating mass and will not need to be ballanced to an exacting standard to achieve an acceptable result.
Saying that i failed pretty bad last time when i converted a Super600 Victa to run Rover ride on blades. Was a bit vibey.
So id probably go with something thats ready made and ballanced elsewhere. lol.
