Funny story about supporting the engine while the tranny mount is off...I have comp. style mounts and and ORD crossmember. Last time I installed a new tranny, I like to get it lined up on the block and the bottom two bolts in, then lower the tranny jack a couple inches so I can work on the upper bolts on the bellhousing. Well, I had the tranny crossmember still out and no tcase on the tailshaft, released the ratchet strap I had on the top of the engine pulling on the front bumper, and went to lower the tranny jack. At the pan, the tranny dropped like maybe 1" and stopped, even with the jack completely released. Those comp style motor mounts like ORD and DIY4x4 sell take a ****load of force off the transmission case and mount when they're coupled with a good crossmember under the engine.
You can bench press those things out by hand. I've done my 203 a couple times and a th350 once. You've got to lower the truck down and lay on a creeper so you're not extending your arms way up above you, but it's not impossible. I'm just a little guy too. However, I finally broke down and bought a cheap tranny jack at Summit for $100 and have not regretted it one bit. It's also makes dropping gas tanks a whole bunch quicker.
Have you considered just rebuilding the case you've got? It's really not very hard and there's tons of information out there, and I know a lot of guys here have done them, myself included. You really only need a SBC cam bearing tool (the biggest babbit driver is really all you need), and a standard set of cheap bearing drivers (great tool to have anyway). The only other fancy thing you need is a clamp to preload the springs for the reverse clutch in the back of the case, but you can make one out of one of those $5 caliper spreaders in like 2 minutes.
You might want to pick up a copy of this book even if you're not going to rebuild one yourself, just for the sake of having it for troubleshooting, reference, etc. It is worth its weight in gold and I would say it is better rebuild manual than any other single book I've ever looked at.
http://www.amazon.com/Turbo-Hydra-Matic-350-Handbook-Sessions/dp/0895860511
