I fitted a new mohair one to mine, makes it easier to use in colder weather as vinyl goes quite hard/stiff. If fitting a vinyl hood you need to either be in a well heated garage or mid summer to get enough flexibility in the material.
There is a chapter in 'How to improve your TR7' on fitting the hood but its quite brief. Its OK if you take your time and mark a centre line on the hood.
There is a pocket along the rear edge to take the mounting bar with studs which go through the rear deck of the car. You then have to drill carefully through the bar blind where there are holes for the hood cover press studs to be pop riveted.
The front header rail needs to be about 20mm open to glue the material on so that it stretches when being closed, although that may be a little less for vinyl as it has less give. There are metal strips in the seal on the header rail which need to have the rivets drilled out to remove before fixing the cover and then re-riveted back on. IIRC these are quite small rivets. I found the most difficult bit to get tidy was the corners of the header rail where several layers of the material overlap as it is folded around the curve.
Obviously a very brief overview, I took about a full day over 2 days to fit it. Much becomes obvious as you do it. Note, I don't think the replacements come with any instructions, mine certainly didn't and I have heard others say the same.
Saab 9-5 2.3t Vector Auto Estate Stage 1
Saab 9-3 2.0 SE Turbo Convertible
'81 TR7 DHC