I purchased the H54 blade last weekend. Unfortunately, I have been working a lot of overtime at work lately so I haven't been able to play around with it until just tonight. The blade frame mounted up to newer tractor just fine without any trouble. The lift link that was sold with the blade was already bent, the seller said he got the blade package with an old Case that he bought used but it was a 200 series. So, someone had "adjusted" the link to work for a smaller tractor than what it was intended.
It is not my intent to take issue with your wording here but rather to just clarify a point for anyone else who reads this thread. A 200 Series Case should never be considered a "smaller tractor". The only difference between a 200 and a 400 is that it does not have as much ground clearance. Therefore, the entire tractor sits 4 inches lower than the 400. And yes, width-wise it is a bit narrower. The H-54 was designed to be used on the 400 Series tractors but it was an OPTIONAL blade for the 224. The only reason it was not recommended for the 210, 220 and 222 had to do with the engine HP. Even though the 222 and 442 shared the same 12 HP engine, the larger displacement hydraulic motor on the 442 provided a bit more torque to the wheels.
What you have discovered regarding the clearance issue comes as no surprise but as I said, the problem is not insurmountable. The H-blade's Mule bracket is considered by many to be stronger in design than the J and later bracket. Most of the blade thrust is placed directly on the Mule assembly and not on the lift arm. Your primary concern should be with constructing an arm that gives good clearance through the entire range of travel so that accidental contact with the hood cannot be made. Heavy wall pipe should be more than adequate but a length of angle iron welded to the outside of the arm to create a V laid horizontally will stiffen that pipe to the point of zero flex.
The link COULD be used on my 1988 448, however, the clearances with the bell plate, oil return line, and the angle that the link operates is not ideal. There is enough clearance to use it to plow but my guess is it would wear out prematurely. I still plan on making a new lift link that is appropriate for this tractor where the transfer of force from the bell plate is straight forwards to the lift arm rather than pushing with an awkward and potentially binding angle. (it would be easier to explain if I could figure out how to post pictures in here) To use the existing bent link, I would recommend inserting washers for spacers between the lift link and the bell plate (as mentioned earlier in this thread) and I would also bend the end of the link at the blade lift arm so it wasn't crooked on the pin.
When I build the new lift link, I will share the design at this thread. Hopefully before September.