A 500D won't give the same results as an A1 regardless of which lens is used as the sensor is smaller than the frame size of an A1.
A 50mm lens on a 500D will give a slightly shorter than 85mm field of view (FOV) than an 85mm lens on an A1 will give, however it's close enough (80mm) to satisfy many people. But, as the focal length affects depth of field you won't get the same shallow depth of field effect from a 50mm (for the same subject framing) that you're used to unless you use a wider aperture. You also won't get the same degree of subject compression as that is a characteristic of the focal length of the lens which is the same regardless of FOV. If all 3 of these characteristics of your lens are important to you (FOV, DOF and compression) then a 500D will disappoint you and you should consider a full frame body, such as a 2nd hand 5D as suggested above, instead.
I keep posting about this, but it's an urban myth which needs to be dispelled! Focal length does not affect depth of field, magnification affects depth of field, and so long as the magnification is kept constant then the depth of field will also remain the same regardless of the focal length.