I have removed my M-20 from my 69 and my bellhousing number is 3899621 which as i understand it should have a 403 so my question is what size clutch should i use and is there any disadvantages to the 621 housing in my car and is this correct or did all 302's have the 403

Jim, I am an old Buffalo guy! Nice to see the folks from my old 'hood here on T/C.

The "403" is for the 10-1/2" clutch that was stock on a 69 Z/28. The "621" was used on SS models in 69. I switched to the 10-1/2" setup from the "621" setup a year ago. You need the "403" bellhousing ~$50 and the smaller flywheel along with the clutch assy. You will also need either a new starter assy or just buy the correct starter nose cone and do the swap. The stater brace is different as well. Otherwise, it is a simple swap. The "621" is easily worth twice what the "403" is worth.

For once, the 69 Z/28 parts cost LESS than the stuff on your car!!! ;)

-Mark.