I have a stack of flywheels. How can i tell which is right for a 383 4 speed. Do i just pick the ones tgat match crank spacing?

It depends on which year 383 your wanting the flywheel to fit on properly with the bell housing, pre 1967 I think they only offered 10.5 clutches in passenger cars, beginning in 1968 I think they started offering the H.,D. 11 inch clutches on the 143 tooth flywheels and matching bell housings
Mopar change all the V8 cranks in 1962 and up to 6 bolts flanges(except the 426 hemi 8 bolt motors) and moved the flywheel closer to the back of the blocks and switch the gear drive starters at the same time.
IHTHs

Oh boy

383 4-speed will be a 130 tooth 10-1/2", pretty simple if you tell us what car and year...

Its for a stock 69 RR

It is year based not motor except for hemi. Has to match the bell housing. The 69 would be a 143 tooth. 70 is when they moved to the 130 tooth FW for Big Blocks and Hemi. Then you need to match it to the crank. Internal versus External balance, and there where cast crank FW too.

Do you have the bell housing and the transmission yet ? Just measure and count the teeth and make sure you have the correct bell for your flywheel and input retainer pilot.

Gus

11” 143 tooth and matching bell for 69 383. But any 318-340-383 10.5 flywheel will fit to with the right bell. Do you have all the bellhousings?

The reason you start with bell housing is starter engagement to the flywheel diameter. A stock 69 RR with 383 would have had the 69 bellhousing and the 143 tooth flywheel. If that bellhousing is correct for 69 or even 68, then you get the 143 tooth, turn them over and post a picture of back side. Internally balance 69 383 motor would have a fw without extra large holes partially drilled to compensate for an externally balanced motor.