Need books for IH 990 Mower-Conditioner

I have a 990 and I like it but I don't have any other frame of reference . It's the only one I've ever owned and I've only had it a year . I had to put a couple bearings in the combination drive and all new tines on the reel , readjusted the reel and the roll gap and tension , rebuilt the chain tensioner , put new seals in the gearbox ( also put in new bearings there since it was open ) , all new guards and a new cutter bar that I haven't installed yet because the old one works good , reset the register of the cutter bar since it was almost a 1/4 of a section off and I still have some misc. welding to do on it . It's easy ( more or less ) to work on . Not all parts are still available but the more common wear parts are generally off the shelf , tine bar bushings from IH are expensive so I haven't done those yet . I think that for the price it's cheaper to rebuild one of these as good as possible than it is to buy a slightly newer model of anything else . I have less than $700 total in mine not counting my time ( a LOT of my time :-] ) . I cut timothy , brome and orchard grass mixed with a little alfalfa and so far so good . I cut at about 5 mph . I only cut 6 acres . Still working on the correct roll gap and tension for grass/mixed hay . The book say's about .020 , I have slightly more than that right now . It's just a sliver of light showing through the rolls but it's still to wide I think . It did OK on the first cutting this year but I think it could condition a little better . It didn't break the stems consistantly on the alfalfa . I'm going to crank the tension down a turn first of all before I do anything more to the gap . Which style do you have , rubber on rubber or rubber on steel for the rolls ? I've been told the rubber on rubber are better . I have the steel bottom roll . Good luck with it ! ...Randy