Hi Seachaser,
Okay. I just spoke with TAD and walked through things with them. The basic manicooler, itself, is now $2100 or so. If you order two, they can discount it to $1900, or so. (Rough numbers, don't hold them to that).
The rest of the cost you were quoted was for the "conversion kit". The two really key items in this kit are the intake manifold and the exhaust elbow. There are a bunch of other parts there, but, to my eye, a resourceful person can probably "work those out" without need of the specific kit, e.g. hoses, brackets, adjusting thermostat housing or using different model thermostat (there is a newer version thermostat that doesn't require that grind out, I think), etc.
So, to me, this conversion makes more sense the more of your system is aging. If the problem is really limited to the manifold, then probably just replacing that makes a lot of sense. If it is the manifiold and the exhaust elbow, which would be very likely, the numbers are starting to converge, but it probably still makes sense to replace just the manifold and exhaust elbow.
But, if that heat exchanger is looking rough -- this one-piece solution starts to look really nice. Same is true if the intake manifold is looking rough (but that is very, very unlikely).
I don't know why I don't have a receipt for the conversion kit for my boat. It was clearly converted. And, the parts, e.g. the hoses, look exactly like the ones in the kit. I suspect a receipt was lost along the way (recall this was installed before I bought the boat).
Seaway Marine is an outboard dealership and unlikely to be able to help. Although Perkins Pacific is a big Perkins dealer, they aren't one known to me to do a lot with 3rd party support for older legacy lines after Perkins stops making the parts.
I hope this helps.
Cheers!
-Greg