C.R. I. P. EMD GP18'S

Is there anyone here which is able to answer this question about C.R.I.P. RR's GP18'S? Were these built from ? on EMD F UNITS ,were these trade -ins ? Please see Below.

Tom

Info I found in Extra 2200 South:

GP18/28 roster Ex 2200 South Issue 36 Sept/Oct 1972 of all units built by EMD:
1238-1239 builders # 28631, 28632 10/63
1256 " 26648 2/61
1333-1342 " 25450-25459 1-2/60
1343 " 25683 2/60
1344-1353 " 26933-26942 10/61

SW/GP/SD Tally Extra 2200 South Issue 44 Jan/Feb 1974
GP7 430-41, 1200-37, 1250-1311, 4200-09, GP9 1312-32, GP18 1333-53, No mention of 1338,1339,1256

News Release Extra 2200 South Issue 47 Jul/Aug 1974 about RI selling 70 GP7's and 10 GP9's to M-K to be
rebuilt and leased back- GP7's to be renumbered to 4425-94 and GP9's to 4435-44. Also mentions "odd"
rebuilt units 1238, 1239, and 1256 not affected.
From this I would surmise those three units were originally GP18's and were rebuilt as something else,
perhaps using parts from old F's. RI bought and rebuilt a lot of used units from other roads during the
70's and was known for being creative. I don"t have a detailed roster although I seem to remember a
list of loco dispositions after RI's demise but I'm unable to locate it.

Update: The December 1965 issue of Trains Magazine has an article about RI diesel locomotives including
a roster. GP18m's 1238 and 1239 are shown as being rebuilt from F7B's 121B and 675B in 1963.