An Alpina 500 is a decent frame, but a size 22 is huge for somebody with a 30" inside leg, even though you must have a long upper body. So I'm not surprised you didn't get on with it.
The classic steel hardtail that was one of the first to be sturdily built, rather than race-light, is the Orange P7. I think a size 19 P7 would be good for a 6'/30" rider.
Also an RST 281 is nowhere near sturdy enough for a man of your weight. You need a Marzocchi Z2. Everybody will say that P7s were usually fitted with Pace forks, but a Pace is too wimpish for you. A 1998 or later P7 will take a 1 1/8 steerer.
And whatever bike you choose, get big tyres, 2.3 or 2.4.
Thanks Anthony - your post crossed with mine.
It seems we are thinking on the same lines. In short I might be better off starting with a different bike/frame rather than try to adapt this one?