3.0 to 3.6
 

Im currently converting my 83 sc to a widebody. Im looking into swapping my 3.0 to a 3.6 or a 3.2. Can the 915 handle the power and is it compatible?

The 915 can handle a 3.2 without issue. If the 914 isn't from an early Carrera you'll have to notch it for the Speed/Reference sensors. For a 3.6 it is recommended to use a G50 for all the added torque. Or spend the cash to beef up the 915.

Good idea to do some interior beefup. WEVO has some good stuff.

Bigger wheels
 

Looking at adding 18s and of course bigger rubber to complete the widebody look. Any recommended suspension upgrades?

I put a 3.6 into my '80SC back in 1992. I used an '85 915/73 trans (larger axles & CV's). Have driven it these 19 odd years with absolutely no problems. Now, I do use it primarily as a weekend driver, but drive in a rather spirited manner. Perhaps if you are planning on a lot of track/DE use, beef-up mods may be necessary(and expensive), but for a daily driver, I think a later 915 is adequate. There are many folks on this forum with highly modified earlier motors putting out more power than a stock 3.6 that are perfectly happy using a 915. Just my $.02

I've had a 915(84) with a 3.6 for about 10 years. I did beef it up with the single "turbo" retaining ring. I run 85-86 drive flanges and axles. This is a track only car so lots of power to the tranny. I put a Varioram 3.6 in a 74 and the input shaft broke. Porsche improved the design in 80 or 81 and these hold up well.