Hi Vick, my 182/180 is a 1960 182C. The 1960 & 61 182's have a similar airframe as the later model 180 & 185's (three window side and a few more inches of backseat headroom) with the exception of the slant tail. I bought it with the sole intention of converting it into a Tw on a one time STC using factory 180 & 185 parts. Last year a gentleman in Florida obtained a multiple STC for converting 1956 thru 1961 182's and I bought the first one, making it a lot simpler.
The conversion STC calls for all Cessna parts right out of the 180 parts book and also required installing a straight tail fin and rudder. It was over my head but any airplane mechanic that has any tin can repairs under his belt would probably consider this a moderate challenge at best. Again I'm not that talented and was only chief rivet driller and bucking bar support. Hope my insurance pays for those new hearing aids I now need.

My friend Steve from Steve's Aircraft (Gascolator fame) was my boss on this project and had more time saving short cuts than I could ever dream up. (Someone once told me I wasn't the sharpest tool in the shed...what he mean by that

)
If you or anyone would like more detailed information or have specific questions I'd be happy to share them, especially if I can save you heartburn on what not to do.
It was a lot of work but for me I'm glad I went this route. The plus is I got a NDH airframe that hasn't been molested. I guess the negatives are it's still considered a 182 by the feds when trying to get additional STC paper work. We asked the FAA for a verbal OK for installing a Pponk kit on this airplane and got a "No it's a 182 you can't do that", but I got a quick OK from them when I installed G/Y 26" tires because they indicated no STC was available for this combination. Go figure!
Roger