$300, 193,000 miles, and spraypaint.

[Mux213]

Hmm, to put an RX7 axle under a hachi you need to start by finding someone who knows what he's doing. First to get a good judge whether it will fit or not (not to wide or to short) but installing it is alot of work. Doing it with just a floor jack would be a real challenge, I wouldn't say impossible cause I've seen people do wonders with cars on floor jacks, but I don't think it's the best approach.

Basically to install the axle you're either going to need to weld brackets onto the axle that match up with the 4 links on the hachi or adjust the brackets on the hachi itself (the latter one I think would be impossible on a floor jack, this is very precise work).
You also need to change the drive shaft, basically make a combination of the hachi's drive shaft and the RX7s one. On one end it needs to fit the Hachi's gearbox, on the other the RX7s axle. This is a matter of taking very accute measurements, taking the axles to a machine shop, and getting someone to do it for you.

You are also going to need to figure out a way to make the suspension work. Either by welding on the right bits to the RX7 axle, or looking into a full coilover upgrade and going fully custom on this one. It really depends on how well the standard suspension points on the RX7 axle match up with the Hachi.

Last but not least, you're going to have to figure out how to hook up the brakes.

So again I stress, you should find someone who's done something like this before and advise you. Seriously, I think you'd be doing alot of work that would be better spend finding something that is a near direct swap (like a GT axle)

Shame the RX7 is become in such a bad shape, if it had been stored a bit better, it could have been one heck of a ride. If the engine is still good, maybe you should sell it, these engines make a lot of money...

As for your speedo problem, join the club Its an old 80ies car Atleast you wont be getting any speeding tickets

Suspension btw, I doubt you can use something from the RX7, totally different cars in that respect..