The Classic instruments SN16F kit should work for you.
Replaces the cable output of the T-5 and has a 16,000PPM (pulse per mile output)
Your Smiths gauge is adjustable to 120,000ppm.
https://www.summitracing.com/parts/cin-sn16f?rrec=true
Wiring setup pages 1-4
https://static.speedwaymotors.com/pdf/275-820.pdf
(See the note below the Smiths connection chart for the Red wire for the sender to get power to function)
"Note: Red wire connection is only required for
some 3 wire sensors. Connect to 12volts for NPN type sensors"
https://www.caigauge.com/documents//...2-460-3028.pdf