Yep Sorry Tonio, Dom is not telling porkys, you are only allowed to play with the fork internals, so any additional preload you may want has to be done with internal spacers.
The best shock to go for if you can't afford an ohlins would be a showa from a 900SS/900SSie. It'd definitely need re-valving/springing for your weight, but it's a good shock. You can always keep an eye on ebay.de, that's where I picked up my NCR shock, and I've seen a few White Power shocks on there for good money.