tranny and rear end questions

[Green72GMC]

Would your truck have a ton of power in first and second if say you took a 250 6 cylinder 3 speed transmission and changed the bellhousing to fit a smallblock V8(If possible?) and put a 305 on it with a rear gear ratio of between say 3.73 and 4.11?

Reason I am asking is Im trying to figure out what kind of tranny and rear end the last owner put in it. My dad said it is probably a 6 cylinder tranny, and I looked up what the truck came with and it was a 250 6. The truck can lift the front tires off the ground about 6-10 inches in first and tops out at around 90-100 (what my friend said when he was in his, I got no speedo).

PS: What would 3.07 gears do to the top speed? Make it go faster?