OK, got the AC compressor working by adding one wire which I'll document later and the speedo works as well. A note on the JTEC connectors, they are labeled in the FSM as C1, C2 and C3, they are all 32 way connectors. If you are looking at the PCM, connectors facing you and at the top the connectors are labeled right to left, not left to right. So C1 is on the right, C2 is in the middle and C3 is on the left.

To document this conversion I'm going to post the JTEC connector number then the cavity numbers underneath on the left. The wire color and circuit, then the corresponding SBEC 60 way connector cavity on the right with the wire color only if it's different. Once you remove the plastic covers you can see where the cavities are numbered at the end of each row, this includes the 60 way connector as well so it's pretty easy to figure out. Just take your time, do one wire at a time and double check that you are cutting the correct wires.

C1
2 LG/BK FUSED IGNITION OUTPUT TO 9 DB
4 BK/LB SENSOR GROUND TO 4
7 BK/GY IGN COIL DRIVER TO 19 GY
8 GY/BK CRANKSHAFT POSITION SENSOR SIGNAL TO 24
10 YL/BK IDLE AIR CONTROL #2 DRIVER TO 60
11 BR/WT IDLE AIR CONTROL #3 DRIVER TO 40
15 BK/RD INT AIR TEMP SENSOR SIGNAL TO 21
16 TN/BK COOLANT TEMP SENSOR SIGNAL TO 2
17 VT/WT 5V SUPPLY TO 6
18 TN/YL CAMSHAFT POSITION SENSOR SIGNAL TO 44 GY
19 GY/RD IDLE AIR CONTROL #1 DRIVER TO 39
20 VT/BK IDLE AIR CONTROL #4 DRIVER TO 59
22 RD/WT FUSED B+ TO 3 RD
23 OR/DB TPS SIGNAL TO 22
27 DG/RD MAP SENSOR SIGNAL TO 1
31 BK/TN GROUND TO 11
32 BK/TN GROUND TO 12

C2
2 VT/TN INJ #7 DRIVER TO 17 DB/TN
4 WT/DB INJ #1 DRIVER TO 16
5 YL/WT INJ #3 14
6 GY INJ #5 TO 38 PK/BK
10 DG GENERATOR FIELD TO 20
12 BR/DB INJ #6 TO 58 LG/BK
13 GY/LB INJ #8 DRIVER TO 18 RD/YL
15 TN INJ #2 DRIVER TO 15
16 LB/BR INJ #4 DRIVER TO 13
27 WT/OR VSS SIGNAL TO 47
31 5V SUPPLY TO 7

C3
1 DB/OR AC COMPRESSOR CLUTCH RELAY CONTROL TO 34
3 DB/YL ASD RELAY CONTROL TO 51
12 DG/OR ASD RELAY OUTPUT TO 57
15 PK/YL BATTERY TEMP SENSOR SIGNAL (have to add sensor, I have not done this yet but doesn't seem to affect charging)
19 BR/WT FUEL PUMP RELAY CONTROL (I think you can splice this to C3 cavity 3 otherwise it sets a fuel pump control code but I did not)
20 PK/WT EVAP SOLENOID CONTROL TO 52 PK/BK
22 BR AC SWITCH SENSE TO 27
23 LG/WT AC SELECT INPUT (splice this wire to the DB/OR wire at the AC low pressure cut out switch)
24 WT/PK BRAKE SWITCH SENSE TO 29
27 PK/DB SCI TRANSMIT TO 25 PK (also splice to cavity 7 of data link connector)
28 WT/BK CCD BUS- (add to cavity 11 of data link connector) not sure if you really need this or not.
29 DG SCI RECIEVE TO 45 LG (also splice to cavity 6 of data link connector)
30 VT/BR CCD BUS+ (add to cavity 3 of data link connector)

To finish off the data link connector you'll need fused B+ to cavity 16 and grounds to cavities 4 and 5.

I don't know if the data link connector works yet, I don't have a scanner at home. Hopefully I'll remember to bring one home from work tomorrow.

Also be sure to get the VIN from the donor truck if you want to flash your PCM.

I used a PCM from a 99 5.2 automatic 4WD truck but since the 74 is a stick I expect it to set a few codes. If you want to use a RH trans you'll probably need to use switches for the O/D and TCC or the other methods with pressure switches and such. The JTEC PCM does have outputs for O/D and TCC but without it able to read the governor pressure sensor and output sensor I don't know if it will work. I don't know if they ground the solenoids or feed them by drivers so research that before trying.

Those wires are

C1
11 OR/BK FOR TCC SOLENOID CONTROL
21 BR 3/4 SHIFT SOLENOID CONTROL