1972 dart 318 want to make the tires spin

My old 318 was right at 300 hp. With the old 8 1/4 2.76 open diff it would spin the tires (sorry ... tire) all day. When I put in the Dana 60 with 4.10 gears, I could only get them to spin if I was going around a corner. I have talked to a lot of friends who build cars, and weird as it seems, the lower the gear, the harder it is to spin the tires. I don't believe changing to a lower gear will help you. Also, it takes quite a bit to get a 318 to 325 hp. Has this been dyno'd or is it a guess? I would make sure I had a good stall converter for sure, but the first thing I would do is tune the car. Make sure your initial timing is where it needs to be. Then you won't waste power off the line. Set the total after your initial and you will be set. If it doesn't spin then, do what I did ... buy a 408 stroker. Now they spin until I let off the gas!