I found Dynamic to work really well. I was having some problems with the band not holding 2nd gear and when I installed the Dynamic (after rebuilding the unit) the problem was no longer there. That was over 10 months ago.
TransGo make a full manual valve body kit part number 47-3 which is for a'67-'69 C4.You might try that if you want to modify yours. I have had good luck with the Transgo Shift kit #47-2 but it is not full manual.Try www.bulkparts.com for trans parts.