The C-3826 may be old but it was used for decades as long as the thermal gauges were in use. Based on my 78-81 truck parts book from Mymopar, as late as '78 the IVR was PN 3592899 which superseded PN 2258413 which is the IVR for the thermal gauges that C-3826 was used to test since the early '60's. Bottom line, I think the C-3826 tool is still the tool to use on your '74 and the 244 ohm sender you have is not the stock sender for a '74 Mopar. The values from the '93 FSM are not applicable as Mopar had stopped using thermal gauges by then.