Looking at Richard'sdolly's thread "Settling in my new Dolomite" I saw Bumpa's picture of a rear seat belt reel and thought "mmm, don't think they'd fit my car".
I need inertia reel units that fit further forward than that because of the mid-HF speakers behind them and the 10mm MDF baseboards they and the 6" subs inboard of them are mounted on - in angled housings.
I had some reel units originally in front of some 6" Alpine SPE-1620 co-axial speakers. They was some good speakers, but the tweeters had paper cones that rotted and blew. I did try to find 6" replacements, but couldn't find anything with a low enough profile to go round that brace under the left hand elliptical speaker hole and would take the base. Hence the 4" mid-HFs and 6" subs - I think I could fit 8" ones, but these were easy and v. reasonably priced, and turned out good enough for me - the mids being 4 ohm and the subs 8 complicated the crossover design though.
When I first fitted those rear reels they clamped over the top of the seat squab and bent it a bit - that didn't matter 'cos it were knackered anyway. But as part of fitting the subs, etc., I decided to fit a replacement squab I had. That meant I had to lift the reels up a bit so they wouldn't damage it. So I added some 1" long tubes and longer bolts with Allan socket heads. These lift the reel units enough above the top of the squab not to damage it, and allow easy access to the bolts.
I do have to take the reels off the shelf to take the squab out, but since I can do that without taking out the baseboards to access a nut underneath, that's an easy enough job.
Graham