4500 may or may not have 3-point hardware - if it was a hoe rig from the factory, it probably won't. You could change the rear end to get one, but that's a job and a half. A second tractor might well be easier.
4500 .vs. 4000AG - no contest, the 4500 is the better digger. 3 cyl .vs 4 cyl - 3 cyl better, IMHO. Certainly newer.
4500 has a 27GPM nose-mount pump, and a 20 gallon reservoir (5 in the nose with the filter, 15 or so in the loader frame). The loader (740) is an industrial loader that will break out 6000 lbs and lift 3000 to full height, with a front axle that will support that. An ag front axle is weak by comparison, and ag loaders are wimpy and slow by comparison. No ag add-on pump is comparable to the 4500 hydraulic package pump, as far as I recall. I'm assuming it's got a loader, they nearly all do since the loader frame is on there from the factory.
As for price, condition is everything at this age. Anywhere from $1500 to $6000, "depending". Hoses are easy, seals are moderate, scored cylinders and rams are expensive, as hydraulic repairs go. Back tires are very expensive. If somebody loved it enough to use all 20+ grease fittings on a regular basis, it's worth a lot more than if they used 3-4 of the easy-to-get to ones once in a great while and left the other 16 or so un-touched. If you can't pump grease in them all, they are not happy and have not been used - the the one in the bottom of the main hoe pivot pin (fun to get to, or even find depending on impacted dirt) or the two at the center pivot of the front axle for "not likely to have got used much if not caring for it." Look for slop (forward/back mostly - open it up and put the bucket edge in the ground, then pull/push and see what moves) at the main pivot of the hoe. Look for the power steering working only in one direction (end of the ram may be snapped off, so it only works when pushing.) Look for missing bushings on the king-pins of the front wheels.
I've done a lot of work with mine, and parts can be found, but as with any old equipment, getting it apart to get new parts on can easily be 90% of the battle when things are rusted tight and 40 years old, not to mention heavy enough to kill you (in many cases) and awkward to handle once you do get them loose.
Well I did not get to do "everything" you said.... but the machine did fire up after the pre heaters were ran twice she smoked a little when getting fired up but ran nicely when she was up and running. She sounds VERY strong.
Everything was greased well and maintained nicely. No slop in any pins, on loader or backhoe.
Transmission worked nice it was a 4 speed forward and reverse with the quick throw lever (i do not know the name of this tranny)
The hour meter showed 2500 or so and i believe it.
The two rear tires have some patches / plugs in them and I will search for those tires for cheap (look for a deal) are they split rim, how do you mount them?
The two front tires were shot and a tube is popping out on one of them.
There are no leaks on the machine except for one seep on one hose connection for the stick on the backhoe.
I got some numbers here.... i will try to look them up too...
on tranny? 357e-4033a
Any info would be great along with size of front tires i could not read the size... cause i need those bad - wonder if i can mount those myself with my harbor frieght machine
Thanks all Kenny