Here's what I did in October on a Ducati S2R 1000.
Arrived at Sadao land crossing. Got my passport stamped out from Thailand. Showed my green book and passport to one booth at Thai customs who entered the details into their computer and printed out two sheets.
I handed one in to another Thai customs booth upon leaving and retained the other for re-entry.
Finding the 'correct' booths here can be a bit of a runaround.
Got my passport stamped into Malaysia and showed the Thai customs printout to Malaysian customs who then waived me through without even looking at it. No questions or paperwork from them which seemed strange.
I've heard that I should've bought Malaysian Bike insurance. Well, whatever!
On the return leg, stamped passport out of Malaysia, approached Malaysian customs who again waived me through with barely a glance.
Stamped passport into Thailand and and submitted the second printout I had previously recieved on exit to Thai customs. After a cursory glance at the bike, passport and green book, I was through.
I'm sure that I missed a few things on the Malaysian side but they were too busy elevating 'not giving a shit' to an art form. Don't you love SE Asia? 8)
Singapore will certainly be a different experience.