I, too, have a '74 140 engine in my '64 544. The PO had it rebuilt and used the older intake and exhaust. I like the double outlet exhaust manifold, and the exhaust seems to keep up with the engine as high as I will rev it.

As for a heat riser, I was pleasantly surprised when the car started right up on December 30 when the streets were dry and I took her for a little spin. Although it was about 32 degrees out, I could get the car to idle within 15 seconds of starting it.

Now I'll have to find time to fix the tiny (a wee bit of fog on the windsheild) heater leak that I had suspected and confirmed that day...
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'96 855R,'64 PV544, '67 P1800, '95 855, '95 854, the first three are mine, heh, heh, 405,000 miles put on 8 bricks