Anyone have any suggestions for heat exchangers that will work well with a 3.0L. Or...Can anyone suggest an alternative to get some heat in the cabin while using headers?

The best if you can still get them…

https://914-6werkshop.com/shop/products/

Some people are happy with the seat heater kits from 914 Rubber and CAMP 914,

I have no personal experience with either. Just letting you know of another option.
My 3.0 6/GT has headers. I keep a coat, hat and gloves in the trunk at all times. YMMV

The stock 914-6 heat exchangers are fine for a 3.0. But if you really want to get something nice, contact Ben (MB911) for a set of his SS heat exchangers. They are a work of art and you will not find better made HE's anywhere. I have his complete exhaust on my 6 and just love it.

Mine are NLA. The volume and cost of materials killed them off. I am completely out of the exhaust game with the state of things. Maybe again some day

Another method would be to figure out how to mount a small china diesel heater in the spare tire well. Run the heat tube under the tank and tie into the defroster hoses. The factory gas heaters went over the tank with a wide thin plastic duct, not sure where it tied in, likely a T into the air/fan box.

Yes you would have use a small tank for diesel, but they run good on diesel.
Don't use the gas heater (china), guys haven't had much luck making them run right.

I ran factory heat exchangers on my 3.2 and it ran fine. But there was a noticeable power / acceleration difference when i upgraded to Ben's 1 5/8" heat exchangers. I would recommend MSDS 1 5/8" headers with seat heaters, otherwise the dansk 914-6 heat exchangers will work. B&B also makes 1 5/8" heat exchangers, but the fitment and heat is very poor.

With Ben out of the game, I'd stick with headers—and go with MSDS Inc.

As for heat, I only need to keep occupants reasonably warm and the windshield clear, so I'm probably sticking with headers. Also, "heat bleed" down the longitudinals and into the car was a thing when I had a four with SSIs, even with new flappers. Wasn't great on hot days, so I bought seat heaters and ordered this to play around with:
https://www.amazon.com/dp/B09N6KN65L?psc=1&...product_details

It just arrived, and easily fits into the space on the passenger side of the gas tank w/o a windshield washer reservoir. Or maybe it goes under the dash—the more heat in the cabin, the better. Thinking about a factory rear defroster switch to turn it on/off. The draw (and safety!) has yet to be figured out with heated seats and decent audio. I'm running a high output 911 alternator, but…

I am glad I bought Ben’s exchangers when they were still available. Well made and only required a slight tweak to adapt the stock heat valve/flappers to work. While they felt pricey back then I’m feeling proud I bucked up.

I am thinking about developing a bolt on heat exchanger for msds headers. Just and fyi.

I thought of doing that too. Sheet is much easier to work with than tube.

That would be great, two great products combined!

I've thought about this as well, likely can be done, but the clearances with the trailing arms are tight when up on a lift, the right side has only about 3/8". Also the pipes are not on a flat plane, so it won't be just a simple box.

Interesting.

The one downside with any sort of electric heat is cold weather with the top off. That was one place where the SSIs really excelled, day or night.

It feels like cheating in a good way.

Fwiw, I was looking at Marty's new 914-6 GT-style headers, and wondered if the long straight extensions for standard sport muffler would work with an aviation heat muff or similar (or something better?).

Immediate downsides include longer path to get heat forward and/or packaging…if it's even possible…

I will take a single side bolt on heat exchanger for your headers

Hand's down....Ben's heat exchangers were the best no question.

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