Frame help!

[bbcmudtruck]

I've been working on my 69 sb for a few weeks now and discovered that my frame has been shortened... They person who did it, did a very nice job on the cut and weld as well as the diamond shaped reinforcement plate. However this has me questioning whether or not my frame is a 67-72 or a later model such as a 73-87. I have searched the frame everywhere for vin numbers, but I cannot come up with anything solid. The number right in front of the power steering pump is only partial and the number on the outside of the frame under the driver door doesn't seem to match up to anything that I can find. Is there any physical differences that are easy to spot to tell me what year of frame I have? I need to replace the lowering kit as the springs in the front have just been heated up to my knowledge. Also, the rear has leaf springs and has had the leafs relocated under the axle. I need a c-notch kit to clear the axle as it travels and there are two options- 67-72 and 73-87 Any and all help is appreciated!
Thanks!!