I've got a real 914/6 exhaust manifold with the heat exchanger removed /. It is rusty especially toward the collector . This would be a good jig set-up for a custom system because the first 2/3rds are correct.
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What is the weight estimate so I can take a look at shipping cost?

I'm coming up with $300ish via UPS 48"x24x24" package at 30 lbs. That seems a bit high since I know I've had some donor sheetmetal that was near that weight dimension but wasn't $300. I'll call my UPS store on Monday and see what they estimate at.

At what dementions does UPS go 'over size'? Better rates at FedEx with an account.

Should be way less. Ben sends out his ss heat exchangers for about $65.
Edit- the box is way too big and sending you into oversized $. The length is correct but once the pipes are ziptied together, the with should be about 24” and the height no more than 12. I sometimes struggle with finding the right size box and dislike making them but oversize gets really pricey.

Those will ship in a 48×10×10 box and should cost about $40-$50 anywhere in the US.

Yep.