hi Southtowns27
your original truck taillight used a #1129 for the stop and #63 for tail
usually folks replace these two with #1156 for stop and #67 for tail
both these bulbs are identical in appearance and shape, however they are both hotter bulbs, but these were the common available bulbs to use without ordering special sizes and they are both still common to this day.
the taillight is smaller globe, G6, but the stop bulb is further back in the housing and is a normal larger S8 globe and it does fit in the original housing, it is quite close to the lens but that's how it came from GM.
1129 6.3V 16.8W S8 lamp, BA15S base
1156 12.8V 26.9W S8 lamp, BA15S base
63 6.3V 4.4W G6 lamp, BA15S base
67 12.8V 7.9W G6 lamp, BA15S base
-s
