saab (t25 model) turbo is generally a garrett TB2569. I can't find any information about it's dimensions, although I can be confident it's smaller than (for example) a GT2554 I think.
This gives you the physical dimensions of the GT2554, so if you've room for this, I'd say you've room for your a TB unit:
http://www.turbobygarrett.com/turbob...1171_3_new.pdf
Only way to tell would be to measure it of course - and then modify to suit. What is the usual issue with the cituning manifold? Turbo too close to the block? Can this be resolved by rotating the CHRA?