The S-10 T-5 has a pretty low 1st gear. That is what will stress the rear end. The flathead gearboxes used to be the fuse that protected the rear. It is not the horsepower but the torque and shock load that kills stuff. I wonder how you will find an open drive conversion for the A rear. A later rear would be more reasonable.
http://www.hotrodworks.com/product/1928-1932-ford-open-drive-line-conversion-kit/ I have an open drive conversion for 40-48 (6 spline) in the classifieds, and also have ring gears machined for 28 spline side gears if you want to do a 9" ford axle conversion.
When I was a snot nosed kid (60 plus yrs.ago ) I tore a couple Model A rear ends out with the 4 banger ,but I was really trying. You need to try to up grade it some way. 300 horse power out of a flatty and were going to Bonniville. `I have a pretty wild flatty and its most likely 225 at the most. On e85 me and car 2000 lb or so 105 in the quarter high 12,s.
Stock model A is 40HP. You might get away with up to 80HP if you baby it. In your case you would be better off to use a late model rear end like a Jeep or Ford 8" and adapt the cross leaf spring to it.
If we are going to use a 292 Chevy your rear will not last very long if you punch around on it very much. Better get a 8 or 9 inch ford ar so
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