Although that brochure does muddy the waters with that statement about "hand lay-up foam core and fiberglass method," I did actually find an original section of hull about 6x8" stashed away in a storage compartment, that seemed to be some sort of "message in a bottle" from Capital Yachts....marked with the original Hull number, what the engine was, and it was spelled "Unibersal" instead of "Universal," seemingly written by a possible spanish-speaking Capital Yachts laborer doing the hull, and that section was solid fiberglass.
However, I ended up side-stepping the whole issue of whether I had a cored hull or not.
It turned out I was able to use my old depth sounder transducer to feed to my new Lowrance LMS-525c (I got that instead of the Eagle, because the LMS has NMEA2000 networking capability and the Eagle doesn't), and it works perfectly!
Either a previous owner, or maybe Capital Yachts, had installed a Moor digital depth sounder with a single-frequency (200Khz) through-hull transducer in my 83 Newport 27-S MKII..
When the depth sounder went dead 6 months ago, just blinking random numbers, I contacted Moor to have it repaired. They had me ship it and the transducer (which is REMOVABLE WHILE IN THE WATER, thanks to a dummy/service plug !!!) up to them in NY, where they reported back the head unit was fine, the transducer had died. I told them I was thinking of buying a new graphic unit anyway, like the Lowrance or Eagle, and asked whether I could use their transducer (If I bought a replacement) and feed it to both their unit, and a new Lowrance. They didn't know, but referred me to the actual manufacturer of the transducer, Radarsonics.
RadarSonic's head engineeer Max said "sure, no problem, but you can't send to both units at the same time, I'd have to put together a switchbox for you." So he did, and I got a new dual-frequency transducer from them to feed the LMS-525c and old Moor unit (the Moor doesn't mind, it just ignores the 2nd frequency), installed it all, and it's using the original Moor through-hull mounting, and it all works perfectly....I can switch back and forth between the Moor and the Lowrance and they are within .1 digits of each other in accuracy. Max, who has been designing and building transducers for 30 years, tells me "...there is no need for any calibration of the transducer signal between units....they just work"....and they do!
The only limitation is the Moor does not like being switched "hot," you need to switch the transducer feed to the Moor before the Moor is powered up, but other than that, it all works perfectly....and I now have GPS charting on top of dual depth sounders, thanks to the Lowrance unit.
Custom Switch box and dual-Freq transducer total: ~$180 !!