That's a good price!
I'd paid £257 for a complete set of 1991 forks, but that included the brake calipers, discs and front wheel. But that was an EBAY auction.
The 1991 USD top bearing is the same as the SV, so a straight swap. You'll have to get the secial Twin works top bearing conversion.
Funnily enough I was thinking of doing exactly the same as you regarding the risers and renthals. I was thinking if you get an engineering shop to do it, I can't see any problem doing this?
Otherwise just buy a streetfighter top yoke conversion.
Let me know if you do this, because I'm still waiting for my front end to arrive
