garage gantry hoist

First, let's establish the height in some recognizable units.

Is it 7 feet 6 inches?

Then, let's determine if the leg width you want is parallel or perpendicular_(probably) to the axis of the hoist. If we looked at the hoist from one end would the legs resemble an A?

Yes, 7'-6'' is the height, and if you looked at the hoist from one end it would resemble an upside down T. To the other response, eventually i will be adding some locking casters to make it mobile. The crane will be made of 2-1/2'' square tubing with 3/16'' wall. Thanks for the responses.

You aren't using 2 1/2" square tubing for the horizontal member, are you? If you're going to pull a 500# engine, you'd better stack two lengths one on top of the other and weld them together.

I'd make the base the same length as the uprights. Probably gusset the joint at the upright/base.

I just stole this: this from phoenix911 on another post. It might help. I haven't looked at it

Thanx for the info, the horizontal member will be constructed of four 2-1/2 inchers, just making it this way because i got a bunch of it for free from a bridge job we just completed, so it won't cost me a dime, otherwise i realize this wouldn't be a very economical way of making one of these.

Whoa! I was gonna suggest three, but thought that with 3/16th wall tubing that'd be overkill.

Did you check out the link I stole from phoenix911?

I recommend that you supplement the base of the inverted "T" with tall triangular braces reaching to the ends of the legs.
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I'm not sure what you mean by "gantry crane". I assume you want a lift point over the car. Does the lift point have to be on a trolley to move the lift point from side to side? Do you want wheels on the base to be able to move the lift point backwards and forwards?