Super Six, Slant Six Timing

Keep in mind that on a slanty, a poor tune versus an on-the-money tune, is not a whole kick in the butt. You might find 10hp or 15ft lbs.
The #1 quickest, most noticeable, kick in the pants/smile on your face mod you can do, is to change the rear end. Most slantys come choked with 2.76 type gears. A swap to the go-to 3.55s will up the giddy-up to;3.55/2.76 = plus 28.6%.To get that on motor only would require something like 225 x 1.285 = 289 cubes.To make that in the motor only would require an increase of about 40 horsepower. To get plus 40 hp from a slanty is not easy, and most definitely, not cheap!
The #2 quickest way,is to find a tranny with the wide gear ratios; 2.74/1.54. And
The #3 quickest way, is to combine the two.

For instance; if you currently have a 2.76 and a 2.45low-904, then your starter gear is 2.76 x 2.45 = 6.76 with a TC of 1600, this is downright snail slow.
But swapping to 3.23s and the 2.74low, gets you a starter gear of 3.23 x 2.74 = 8.85. And this would be 8.85/6.76 = plus 31% increase in take off torque, while increasing the hiway revs just; 3.23/2.76 = plus 17%; or from about 2400 @ 65 to about 2850 with 25" tires.
Now go back and re-read that part about plus 31%. Plus 31% is HUGE!! This will make your lowly 225(3.7l) take off like it was a 295! Thats nearly 5 liters!If your head can't get this, you have just got to try it!
And the part I didn't mention is that the 2.74 tranny usually has aTC with a bit higher stall. And sometimes a loc-up, too.You will need a tach and/or a rev-limiter

If your car happens to be one of those with 2.45 gears, and you do the swap,wear a diaper on your first trip out!