Looking at images online of 914's, I' noticed smooth color matched targa tops. How are they doing this, are they using a fiberglass cap over the existing top or are they using filler and sanding them smooth? Can someone enlighten me on this?

You can sand the existing top smooth, prime, and paint. Use rough/medium sandpaper to get grain down then use fine sandpaper to finish. Don't be in hurry. Take your time, go slow with the sanding. The fiberglass top is much softer than steel.

Just don't go too deep or you'll go through all of the coating.

I've done this on five of my cars. Take your time and block sand it smooth.

I just did mine and I put a skim coat of filler, then sanded. Ended up sanding all the way back though the filler before I was happy with the finish. I didn't take my time and you can tell, but still looks really good.

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Nice!! What color blue is that?

my car was fitted with a thicker, smooth, reinforced top as built in Germany -

a prototype item from Werks 1 - so clearly there was a factory mold for this back in the day

- NOT a sanded down 4-cyl version

it is about 9 lbs heavier than the stock top, has alloy reinforcement bars embedded in the 'glass around all 4 sides, and is 2-3mm thicker overall -

.

Bahama Blue, it's an old GM color.

And it makes them go faster...

I've sanded through the gel coat
you will get spider cracks every 6 months if you do

the only way I was able to put a stop to that on mine was to take it to a fiberglass manufacturer and have them re gel coat it

so be careful... sand lightly..

Glad you brought this up. I mentioned this before, but if you do go to sand it down and especially if you go through the gel coat, you should still expect to skim coat the top with filler and re-sand. Once the gel coat is compromised, the resins/gases still trapped (yes, even after 40 years) inside the fiberglass will want to escape through the paint. As Brant mentioned, it's either lay down another layer of gel coat or skim coat with high quality filler.

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I like the painted top.