Puttingh a different engine in a '73 Silver Shadow

I got an old Shadow that unfortunately came out of Florida and the floor pans are rusted out so not much value in the car. The engine ran good when I got it and then I let it sit in my shop for 3 years since I never had the chance to cut out the cancer and drive it.

Due to the super expense of engine work I thought I would just put in a 350 and hired a mechanic who claimed he had done a swap on a Rolls and he could do anything. He was incompetent and he had the car in his shop for 2 years trying to get an engine to "fit". I finally got tired of his BS and had it towed out of the shop and he had a Dodge 360 sitting in the engine compartment when I got it.

I had moved out of State and my new neighbor is an old Hot Rod mechanic, used to be a foreman for the City's fleet of vehicles and this guy knows his stuff but has not worked on a Rolls before.

We are concerned about engine mounts since the original engine (It is for sale in case anyone wants to buy it, and the Dodge engine too) was mounted at the bottom up front and then to the housing of the tranny which I assume is a Turbo 400 which I was told was stock out of the factory.

I heard also that a 350 swap is not new so instead of trying to reinvent the wheel, was wondering if anyone knew where we could get engine mount modifications to secure this engine ( or any other engine suitable for this car). I remember reading in a forum that there is a company that makes an oil pan that is not so deep which would have to be installed if using the 350. Any tips would be appreciated, thanks Ray