has anybody used this pressure plate and is it any good its for a 91 ser lookin to make 300whp

I've had one for years. I think it's a great item. I don't know if it's rated to hold 300whp, though.

I'm sure it depends on what disc you're using with it.

Throwing a 3-puck disc onto it instead of a full-face isn't going to make the clamping force of the pressure plate any higher, though.

The clamping force stays the same indeed, but the disc makes a difference. As an example, an ACT Heavy Duty pp mated with a Street Disc will hold ~250 ftlbs. The same pp mated with a 6 puck disc will hold over 300 ftlbs.

Aren't we talking about a JWT pressure plate?

Yeah, I was just using ACT as an example. My bad, I edited the post to be a little more clear.