R66

You need to give us some pictures of the starters and bell housing or at least tell us if you have a 153 tooth flywheel with a 10-1/2" clutch or if you have a 168 tooth flywheel with either the 10-1/2" or 11".

I can't understand why the starter would move around unless it is not tight. Also 3/16" thickness for the block plate is a lot more than any I have for Lakewood Bell housings (1/2 century old).

If no pics, how about Mfg. and part numbers for the stuff you bought.

Right now shooting in the dark.

jim lockwood

The PowerMaster starter has straight across bolt holes. It's been too long since I looked at the other starter to remember accurately.
Hedman 68280 side exit headers.


Pictures always help!

Jim

MikeM

If the starter is intermittently working, I am wondering if the problem is not a bad/worn starter drive?

larrywalk

The block plate won't make any difference in how far inward the starter pinion can go to engage the teeth of the smaller 153 tooth flywheel, BUT, it will make a difference if you have not removed the knockout in the block plate to permit usage of a block mounted starter - otherwise it will block the starter from being mounted inwards far enough.
(Remember that the instructions require this.) In early applications ('50s), bell housing mounted starters were common.