starter problem 454

I have a 1985 Itasca motorhome with a chevy 454. I have verified the engine manufacture date and engine block coding. I counted the teeth on the flex plate and there are 168. The problem is the amount of shimming I have to do to get the starter gear even half way into the flex plate teeth. With no shims the starter gear barely engages the flex plate. I have almost 1/2" of shims on the outboard bolt now and it could use a bit more to get it within 60 thousands. I went through the paperwork that came with the r.v. and it looks as if this is an ongoing problem. The folks at Advance Auto are very helpful but the local repair shops do not want to work on it as it is on a motorhome. Any ideas? Thank you, Ken
starter problem 454

It seems to be the wrong starter. ck with a chevy dealer for correct part no. as a retired mech i have found that in some cases aftermarket parts do have problems at times. Good luck :)