Should be a c-6, if it's a van.

I'm not real sure that the trans was coded in the v.i.n. in 74, but every Ford built during the 70's had a code sticker on the drivers side door jamb. If you could get the trans code from that or get a picture or two (including one of the pan) from your trans. I'm sure someone here could tell you with certainty what you have.
I have a 71 E300 14' box van with a 302 and a C4 automatic. So they did use the C4 in some bigger trucks.
I think all the C4's unbolt from the bell housing, but the C6 does not. There casing is molded to bolt to certain size engines.

the bell housing and trans are all one piece
the only other number on the sticker is
F02197R1234
my feeling is it's a C6
any reason to keep it? Is it a better trans for a V8 swap?

The "Small Block C-6" is getting hard to find and can take some serious torque if in good shape. I took the FMX (heavy) trans out of my 69 351W Mustang and put in the lighter, stronger C-6. I'm putting out about 380ft lbs and there is little or no support for the FMX. There are people out there looking for your C-6.
 
71HANTO