Here's something else to think about. If you are building the gun from the frame up and the frame ramp is cut for the 45 and you decide to build something in the 9 or 40 family the ramp will be over cut and most likely will cause feeding issues.
So besides offering more case support the ramped barrel will be the best way to solve that problem.
Also if the ramp in the frame has been moved to far forward, cutting the frame for a ramped barrel just may save the use of that frame.
I like ramped barrels, however I feel many do not understand the timing issues involved when using a ramped barrel.
As for parts I would prefer top shelf parts that have to be fit, stay away from MIM.
As for barrel design, bull or bushing type, that should depend more on your intended use and what you want to achieve with the gun.
As for the ramp cut in the frame Jim explained that very well. I will add the Clark and Para are not really the same cut, they do look very similar. If you are cutting a frame for a ramp barrel I would choose the Para cut over the Wilson/Nowlin because the Para is a radius cut.
As for the series 70 or 80 difference, again Jim gave you a very good answer.
Regards
Bob Hunter
www.huntercustoms.com