Typically, it's much more work than expected. But not impossible.
What I knew I had to do, was to narrow the sliding rails. Partly because they wasn't centered on the seat ( the outer one was placed outside the seats side) and partly because they was too wide apart for the limited floor space in my car, a 34 Roadster.
At the same time I wanted to lower the seat as much as possible, because I have built the car suited for a very low seating position.
Initially, I planned to keep the manual rise and lowering mechanism. Not because I needed it for adjustment purposes, but becauase I thought it would make it easier to fasten and remove the seats for later, since they are from a 4 door car and therefore don't have a backrest tilt mechanism.
But as my work progessed, I discovered that the seat rising and lowering mechanism was constructed with a huge bend in the complete seat frame. I suppose it is because the mechanism is on one side of the seat, and with a person sitting in the seat, it still rises / lowers equal on both sides! To achieve this I guess they have to add bending forces into the seat.
When I discovered this, I gave up the rise and lowering option and removed it completely. But I kept the ability to loosen the bolts and rise the empty seat up in high position for maintainance purposes.
Haven't measured very accuate, but I think I have lowered the seat app 1,5 inches.
To ensure that the two sliding rails stood parallell in both horisontal and vertical direction during the work, I made a wood jig, that became very useful.