I never follow the manual advice for leveling side to side on a used deck, especially the formed sheet metal decks made late 60's thru early 70's. If you measure the "top of the mower housing" on these decks you will not be getting a true reading. These decks, especially the 48", are very easily warped by previous abuse (using them as a step stool, battering ram, mid mount blade, etc.) and often times the deck skin becomes twisted and contorted. (This is one of the flaws of this vintage IH deck, the gauge wheel brackets were not very well supported and the ends of the deck bent rather easily).

ALWAYS measure cutting height from hard surface to blade cutting edge when leveling a deck, NEVER rely on the deck skin measurement. This holds true for both fore/aft and side/side adjustments.

Last 48" deck I leveled for a friend took considerable reshaping of the deck skin just to get the gauge wheels close to the same height (I actually had to block it up on 2x4's and step on it to get it straightened out). 

Other tips, If you run out of height adjustment at point "C", remove the sub frame and bend the arm that slips over the lift rockshaft up in the air another 1/2"-3/4", you will need a torch for this. The extra bend will lift the subframe higher in the air at point "C" and allow you to properly level the mower fore/aft. Seems IH was pretty skimpy with the adjustment range at point "C" and I'll bet many mowers left the dealerships cutting "downhill" from day-one. 

I also prefer the adjustable links (between the lift arms and the sub-frame) for side/side adjustment in place of the washer method described in the book. They are available from your CC dealer. You only need one (one side) to level most mowers. I always thought that the washer method put much more stress on the rear mount area than necessary, especially considering that IH decks usually crack at the rear attachment points anyway. In-fact, I have had to reinforce both of my decks at the rear hangers due to washers and skin cracking. 

1. Get deck level

2. Set cutting height and recheck level

3. Set gauge wheels so that they are 1/2" to 3/4" off of the ground. (You may want to fine tune your cutting height to make the 1/2"-3/4" clearance as close to 1/2" as possible)

With the wheels set like this the deck rides in the thatch of the lawn. This takes out a lot of the bouncing and rough riding associated with leaving the deck ride directly on the ground, but also "preloads" the gauge wheels so that they are always ready to lift the deck over a bump or ridge.

Keeping them down in the thatch prevents the deck from streaking when the wheels lift it because the difference in cutting height between the slung deck and the wheels is only 1/2" or so. This is where the spring assist trick really makes a deck work...you can ride on the ground with a feather light "spring" touch, always ready to float over a bump.

BTW, the front gauge wheel will always ride high at "normal" cutting heights. It's purpose is to save the lawn/blade on those big scalps, not to control deck height.

Level the mower side to side and fore and aft so that all of the blades are cutting the exact same height (measure from blade tip). Measure each blade both "inline" with the tractor and perpendicular to the tractor.

I like my decks to be dead level (same measurement front and back), some will say run the front of the blade 1/4"-1/2" lower than the rear....1/4" nose down. I think that this promotes scalping, but do what you think is best.

Check for washers/no washers under the blades, this will cause spindle to spindle cutting height changes.

Check level with the belt on and tensioned...sometimes (especially on 38" and 42" decks with the big center blades) the belt tension will "tweak" the center blade adjustment.

If the skin is not square/true use any and all means at your disposal to fix it....shims, washers, hammer, BFH, whatever it takes to get everything in the same cutting plane.

While you are overhauling your deck check for wear on the rockshaft fork, front eyes, and rear hangers. Also check for cracks near the rear hanger mounts, gauge wheels, and center spindle. Fix all problems as necessary...weak areas like those mentioned above make leveling a deck harder to do right and also result in a deck that won't "hold it's level" for very long.

Correctly leveling a deck might take 4-5 hours worth of careful measuring and adjusting (at least the first time), but the results will be well worth it.

Those of us here that have spent time on our decks are rewarded with "showcase quality" cuts on our lawns.

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