I dont mean to discourage anyone here,but being realistic ,I cant wholeheartedly recommend going through all the effort and expense to build a loader for a typical "lawn tractor"..if we're talking about a higher end John Deere,then maybe I'd say it would be more suitable,but I'd still say getting a ractor that was available with a factory loader is a much better choice..
I wont go as far as to say that lawn tractors with loaders or johnny buckets are a toy",that is not true,you CAN do a lot with one,they ARE very handy for certain chores like mucking out stalls in a barn,or light use around a home and garden..but the main reason I'm saying they aren't worth the effort is not so much their lack of lifting ability or
usefulness,as the fact the tractor simply will wear out or break in short order..they just aren't beefy enough!..
I would love to build a loader for use around my yard,it will lift a lot more than I can!..but even on a relatively beefy old tractor like one of my Suburbans,it will be pushing it to the limits,even EMPTY a loader frame and bucket (and the pump ,etc) adds at least 300 lbs to the tractor,before you put anything in the bucket..
I'd expect to at least have the steering gears and compnents fail rapidly,maybe the front spindles would "live" but certainly be suseptible to failure,especially being 40 years old to start with..the transaxles were not really made with earthmoving in mind either,but would probably hold up a lot longer than any of todays cast aluminum ones,especially the lower end hydrostatic ones...
I had a 641 Ford farm tractor with a Wagner "pipe" loader on it,even THAT was rather limited in what you could DO with it..it would lift 1000-1500 lbs,but once you had that or even 600 lbs on the bucket,it was very diffucult to turn the wheels,and didn't feel like it was heavy duty enough,you could feel the front axle flexing and even with loaded 28" rear tires it felt "tippy"..
I'd reccomend buying the right "tool" for the job,a lawn tractor CAN be used with a Johnny Bucket or scoop,etc,but not for very long,without having some major repairs being needed to the steering,frame,and rear axle,IMO..I did build a bucket conversion for the plow on my MTD and it did a lot of work for me moving heavy boulders for a stone wall and dirt,etc..but I definately loosened the steering up a good deal,and I'm sure the hydrostat didn't like the abuse either..but the tractor owes me nothing too,and I'm not overly concerned if I "finished" it off..probably why its still going strong,just to spite me!.