According to a copy of an AMAL ID reference, your carb...389/234 was actually outfitted for a US market 1966 BSA Thunderbolt 650.
The correct carb number for your Trail Blazer is- 389/16
Interestingly, they show as having the same bore size (1-1/8) just different jets and throttle slide cutaways
Needle
Bore Pilot Cutaway Main Jet Position
389/234 BSA 650cc 1966; A65 Thunderbolt (USA) 1 1/8" 25 3.5 310 0.106 3
389/16 Indian 692cc 1958-60; Trailblazer Twin 1 1/8" 30 3.5 270 0.106 2
Theoretically, you could rebuild your carb with new parts to suit and take a chance. OR buy a new one from Burlen and save the gamble.