fergor,
I think you're talking a M101 CDN 1/4 ton trailer, right?
Not sure about the shackles. Most people do the spring-over-axle swap to get some lift instead. I suppose shackles could be done, but it isn't nearly as common as the SOA, which nets you that much lift or more.
I have run my M101 stock on stock tires. It worked excellent.
I then did the SOA mod and had the trailer on 315's which was probably about a 5 inch lift overall- I hated it! It was stable but too tall. PITA to get gear in and out of trailer.
I then reversed the SOA and did a shackle lift that was about 4 inches longer than stock netting roughly 2 inches of averall lift. It is still tall but once I get the tire size down to a 285 I think it will about perfect.
I will try to get a pic of the shackle and lift up later.