I think if you can build your own frame you probably can chop the top..That would save you $1000 to $1500 and you could say " I chopped it"...I don't know what year cab, but I chopped a 48 F1 5" and it was my first chop at age 62.. It was fun and I plan on chopping my A coupe next.. Go for it......
I believe your spring angle must match your axle caster angle unless you have adjustable perches. If you try to adjust after assembled your spring will be in a bind and quickly wear out your shackles........