I am building a stock chasis 70 Challenger with around 600hp. My question is at what power level should I be thinking about a front motor plate? I was going to go with solid motor mounts only. Also wondering if anyone can tell me if I use the Andy F motor plate sold at Mancini, will the alternator still mount in the stock location? Are there any other issues to think about when adding the plate? Thanks for any help or suggestions.

A motor plate will cause some accessory issue's for sure. Those AR Motor plates are nice, but non of the stock pulley's will work any longer.
It just makes it easier to mount the engine and remove it with a motor plate. It also provides more room for headers and oil lines.
At your level, and running the alt and other stuff, just use the factory mount stuff and add a torque strap to the driver side.

600hp use stock mounts with a strap. past that go plate. here is my alt setup with a challenger plate

Thanks for the advice guys. Hey sixpackgut that is one mean looking machine you have. I'm jealous to say the least!!!

No, the stock alternator will not fit anymore in the stock location. You have to hang it below the plate or come up with some other arrangement.

The stock water pump will work fine once you adjust the pulley depth. You can either space out the lower pulley using the 3/8 spacer that Mancini sells, or you can have a machine shop mill off 3/8 on the back side of the water pump housing.

Most guys using motor plates are serious enough racers that they don't mess with stock accessories. They usually run electric water pumps and racing alternators. But there are kits to hang small alternators on the motor plate. I make one of the kits myself and DMI has a low mount bracket kit also. So there are options out there.

Thanks Andy. By the way, I bought your book last week and really enjoy reading it and learning more about engine building. Thanks for writing it.

Glad you're enjoying the book. My second book should be available in a few months.