DIY Heavy-duty steel utility wagon, info needed!

Folks- if any of you guys stumble across this and are DIY sorts with input, I am all ears...

I need a utility wagon, mainly to move my engine hoist and other heavy/unwieldly shit from the garage to the back shed- BUT, will also need to transport a 600+ pound engine back there at some point as well.

Looking to go about 18"X36" for the loadbed, wheels directly under the assembly (ie: the widest point is the loadbed).

I have a good bit of scrap 2X2X1/8" wall tubing as well as angle and such, from past 4X4 suspension and bumper builds. I have no problems or questions regarding the building of the frame...

What has me flumoxed is the steering, and appropriate axle for the fixed and steering axles.

Basically, want this: http://www.weldingtipsandtricks.com/wagon-made-from-scrap-steel.html

It looks like he used solid rod for the fixed axle, and steering knuckles for the steering bit. I don't think the solid rod is up to this sort of stress unless I go larger diameter. I do, however, think that welding grade-8 bolts to the frame itself would work just fine. Yes, they will loose some strength from the heat and welding- in that case, second thought I could through-bolt through the frame (dropping the frame down another few inches to allow this, of course), leaving enough length on the bolt to properly affix my wheels (which will have bearing-equipped hubs). So I don't think the rear axle is such a big deal- anything I am missing here?

The front axle, though: I am flumoxed. I have no idea where to obtain the steering knuckles. I could make the entire front assembly pivot, but this seems like it would be a weak point of the structure, and would make the cart more tippy. I don't want "Radio Flyer" single-pivot wagon steering, looking for something more like a solid-axle equipped truck's steering (ie, the pivots are at each wheel, a la "kingpins" on a Dana axle).

 I realize box-section tubing is overkill on this project. I will use expanded steel for the load deck, or perhaps wood if consensus says this would be better. I am using box section because I have a lot of it that's going to rust if it's not used, so this is a $0 supply. I can buy the wheels if I have to, for $10 per- but I already have a source lined up for wheels off an old commercial lawnmower, at $0.

 Costs for the project looks like a bit of hardware (which I probably already have from previous projects- I have a 200-pound case of misc stainless and zinc fasteners), some paint, and whatever the solution ends up being for the load deck and steering. I anticipate I can do this for less than $50, and some welding time. Harbor Freight has something similar to what I want, for $120, but it's actually much weaker (the 1000-pound rating of their unit is said to be VERY generous).  Yes, I could buy the HF unit and weld on some reinforcement, making it suitable to the job- but that is akin to throwing good money (and time) after bad. I am not a wealthy man, it's time I stop spending on things I can make myself simply to "Have it right-the-hell now". Actually, it's WAY past time I stop doing that, and this goes double for the country at large and most of us as Citizens... but, another discussion, moving on...

I realize the box section will make this thing HEAVY, that is fine. I have some clevises I plan on welding to the frame for tiedown use as well as hoisting use. Hoisting, as in: to hoist it up into my trailer if I need to go mobile with it (which I will- this wagon wil lbe used at my local pick-a-part salvage yard to retrieve axles, transfer cases, etc). I have a milsurp M101A1 trailer that I use behind my S-10 (itself highly modified- Dana 44 solid axles from an 82 Wagoneer are under it, about 12" lift all told), it is of course quite tall. I am modifying it for civvy voltage and 7-wire RV harness, and plan to delete the tiltbed feature and mount a pickup bed hoist in it to allow me to easily load axles, engines, etc. So there are no concerns of keeping this wagon light enough to get into the back of a SUV without throwing my back out. Any finished product under 150 pounds will be fine.

Could use your input on the steering and load deck!