seat height
#2
Everything you need is at ACE Hardware, I'm 6'1'' But I like the front of seat about 10m mm higher, You have to take ALL Bolts out, Get Longer Black bolts & Black Steel Spacers, The rear has 4 bolts I just re-installed 2, It's tough on the back, but makes a difference, gradually thread each one, Don't tighten till All are threaded in.
#3
#4
Just do as ACE stated! You could actually buy steel spacers, longer bolts, and be done. Although that Weltmeister kit are full length rails, the integrity of the seats mounts, lie in their mounting points. Spacers/washers would be fine. Or, if you have access to any manufacturer (that could cut ya something), then make your own rail spacers.