I can give you an example of why we welded mine in on a drive on rack. When we lifted the car on a frame rack, the gap at the top of the fender would open up and the doors wouldn't open. There was nothing wrong with my sub-frame, no rust or rot, it was just a 40+ year old unibody car. Once we welded the connectors in place, I can lift it up and these problems disappeared.
If you can put your car up on four jack stands and everything still lines up okay and your doors work fine, then I say go for it. If they don't, I would put the jacks under the rear axle tubes, and then under the K frame to support the weight of the engine and front sub frame. This would basically be the same as a drive on lift.
The same on a rotisserie, if everything is lining up, weld them in.
