This may help;
K Frame Identification
There should be a small round or oval "coin" on the front with a 2 digit number stamped in it. That will be the K-Member part number. There is also a very small 4 digit number stamped near it. Those small numbers is the date. The date will be like 3229 = 322nd day of 1969.
Here's the 1970-71 K-Frame numbers
10 #2962010 Crossmember (K-Frame) 225 Engine
12 #2962012 Crossmember (K-Frame) 318, 340 & 383 Engines
14 #2962014 Crossmember (K-Frame) 426 Hemi w/ Skid
52 #3583052 Crossmember (K-Frame) 318, 340, 340 T/A & AAR, & 383 Engines
70 #3583070 Crossmember (K-Frame) 198 & 225 Engines
74 #3583074 Crossmember (K-Frame) 318, 340, 383 & (440 w/ Skid) Engines
76 #3583076 Crossmember (K-Frame) 426 Hemi w/ Skid
77 #3466477 Crossmember (K-Frame) 318, 383 & 440 (440 w/ Skid) Engines
View attachment 69981
A-66
Registry