If this is the 86 C10, alot of those truck came with the TH350C trans with lockup converter. The 350 & 350C use different converters, 350C will have an electrical plug on left side.
I've had bad luck with B&M converters in the past.
Rear gear ratio is probably 3.08, not sure about cam size but, if it's 288 Advertised Duration you may need closer to 2800rpm stall converter. Just a quess.