[Carbroke]

Most of the V-8 conversions for V-8 in in the Experimental world use a RPM reducer (most seem to use a planetary unit) with a viscous drive between crank and planetary to achieve proper prop speed at the engine RPM which yields the proper HP and torque to achieve the overall power needed. The ford made 85 HP at high rpm. You will need to cam the engine to lower that.

There are gear reduction axial units made by others that you should look into purchasing, unless you want to completely re-invent the V-8-in-an-airplane scenario. There are also units using cogged belts as well.

They also use as much aluminum accessories, heads, etc in attempts to lighten the power plant.

I would guess the Pietenpol , being rag and tube, would require significant rear off-setting weight to get a balance point within limits. This is going to put more stress on the tail end when landing and in rough field strips. Also, more stress on the front wheels due to engine weight.

I know you are wanting to do something different from what others have done; that's the whole idea of the experimental world. But by virtue of placing that big block of weight into that plane, just be aware that you are introducing the need for modifications elsewhere in the frame of the airplane.

That all said, I'd look into the later flatheads (24 stud versions) for two reasons. They are better manufactured, and there is way more speed parts available for them which will allow you to get a much better HP/Weight factor out of the deal.
you will still likely need to do a reduction gear of some type to keep the blade tips from going supersonic at the engine RPM that delivers proper power.