I recently fixed a friends Penn slammer rod that had a guide broke. The guide was called a spinning guide by a person making a reference apparently because a lot of name name brand companies do this on their heavy spinning rods(using heavy casting guides in place of double foot heavy spinning guides)..i thought a spinning rod would want a high guide from the frame and less wind drag on the cast???..my questions are
1.) do other builders do this, and is it common to use casting guides over all purpose spinning guides or is it just a preference thing.
2.) I also use a #20 or 25 on casting guide on baitcasting rods and some boat rods..is this practical.

It is common on many commercially made rods. Nothing necessarily wrong with it but higher frame guides, at least near the butt, should improve performance a bit. Many of these rods are built for power, not casting proficiency, however.

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Double foot guides will also add weight to the rod

Bill - willierods.com

Thank you for making that clear Tom.

You mentioned that you use 20 and 25 casting guides on some baitcasters. That's fine. If you need the larger ring to get the height to keep the line off the foregrip under load, go right ahead. But you might also consider using a spinning guide for your butt guide on a casting rod, which generally lets you use one size smaller ring and achieve the same height.

This is all just part of custom rod building - think it over, decide if the parts you're using meet the criteria involved, and do what you need to do. You're not limited by tradition or commercial rod production dictates.

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In past times, the butt guide has commonly been a double foot high frame guides on many fishing rods. The biggest reason used by vendors is that it increases the durability of the rod, since that guide in a double foot version is less likely to bend if it is subjected to travel stress.

Be safe

I have built several rods for some one that saltwater fishes
The rods had double foot guides on So i figured cut my wrap time and lighten the rod up I put single foot -- Spiral Wrapped rod
Well the guy rests the rod on the edge of the boat He was Quit Large and sat while fishing and it seems the rod got knocked around and guides got bent So back to double foot

If the rod does not get rough handled you can use them

Bill - willierods.com