what heads are on the 525's?

As far as performance, I dont know there are some engines making big numbers with GIL/Stainless Marine and such.... I would not worry about performance

The trs trans has ears on it that bolt to the inner transom plate, and a trs cafe should have a front and rear motor plate. Even if the 525 had the 14 pin connector merc makes a 14 pin to 10 pin adapter.

how is the rear of the 525efi supported with a trs setup if the inner plate cannot be used due to the tranmission?

525's, 600SCi and 700SCi's have the edelbrock aluminum heads with a "non standard" exhaust bolt pattern.

I thought they were Edelbrock, didnt know about the different bolt pattern....

You can use a rear mount plate and transmission set up . That's how mine was set up. Yes the heads are non conventional bolt pattern. You can re drill header flanges but a manifold is cast and no way possable to accommodate the bolt spread differance. As for manifolds on big motors there are plenty. I had a set of stainless marine on a 1000 hp blower motor. They make a bit more toque on SC engines.