Hi,
Making some modifications to the Sirrus may well be a good idea. I owned one of those once with a 61cm frame. It wasn't a bad bike and I liked the more upright geometry. As I was only riding on roads and hardly ever on trails, I did a modification by putting some drop bars onto it. I had planned to change the brake levers to STI type but in the end I just used the existing setup.
It was running 28mm tyres which were comfortable and I just increased the tyre pressures for road - only use. I rode it like this for quite a while and realy enjoyed it. When I made the change to a full road bike I listed it on
ebay (or perhaps gumtree) and offered the buyer the opportunity to have me convert it back before he picked it up but he specifically wanted it as it was.
Worth a thought I'd say. I've uploaded a photo of what it looked like.