Well, it does depend on which 108 the speedo came from, I would imagine - I would think the gearing in the 6 cyl's would be different from the 4.5's, not to mention the difference if it had MT or AT, M110 or M108, M129, M116, M117, or M130. 108 is a VERY generic term encompassing 250S all the way to 280SEL 4.5 (250S, 250SE, 280S, 280SE, 280SEL, 280SE 3.5, 280SE 4.5, 280SEL 3.5, and 280SEL 4.5). But if the part numbers on them match, then it'll work. Otherwise - no guarantee it'll be right, I'd imagine.

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Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k