TR, put up some pictures of the underside of your Tiger and we can mark them up to show where stuff ought to go. The pipes run pretty much straight from front to back, but from what I’ve seen (having two sets of headers) there is some variability in what you have to do ahead of the frame pass-throughs. The factory exhaust runs under the rear axle – I’ve seen some exhaust shops make over-the-axle bends but there really isn’t enough room to do that especially if you use larger tube sizes.
The others’ comments are fair. Unless you’re completely above board on building a ‘tribute’ car, you’re not going to get a lot of respect from folks in the Alpine/Tiger community. The underbody changes that distinguish Tiger shells from Alpines are fairly well known by marque aficionados and most if not all the intentional clones are quickly discovered upon close examination. Tiger bodies were built as Tigers (by the factory) from square one – there are only a couple of places where an existing body panel was hand-bashed to fit, so there is little or no ‘kit-car’ variability in the body construction that you’d be able to claim to account for discrepancies between an Alger and a genuine Tiger.