Let me first apologize if this is a beat through topic...I have honestly searched for about 3hrs to find this answer, yet every thread I have read never really gives no specific answer. Ex. well my friend did it or I have heard of people doing it.

Im in the process of finishing a 383 that Ive been working on for too many years to count. Anyway the current engine in the car is from a 85 305 TPI and had a distributor melt down (Module is finally decided to quit).

Well after a month of getting a ride from my wife to work, my breaking point has been reached. So last night I decided to throw in my new late model msd distributor and a stock external coil. I got all new connectors (1 two pin and 1 four pin). All the wires matched up perfect. This evening I re-checked everything before cranking it over for the first time and everything seemed fine. I had a buddy with an old spark plug attached to the coil, check the spark. Well I got a good spark, but now my tach is pinned to 7k.....would there be any reason for this other than, I just fried the tach? Ive only run through maybe 7 revolutions of the engine just to make sure that I had fire. The tach is really not a big deal I just want to make sure everthing else is good before I continue to put the distributor cap on and run all the spark plug wires.