cab mount specs before mounting bed?

[MM in NM]

My old bed is now off and i'm slicking up the new bed to go on soon, I hope.. This week I'm going to clean up and paint the rear chassis as well as replace the carrier bearing just because it looks like it'll need it sooner rather than later and it's right there without the bed on.

My questions involve the cab mounts. Common sense tells me that in order to get everything aligned later the rear of the cab (and the front) should be a measured distance from the frame. Being a New Mexico truck the old stock rubbers are kinda dried out but not cracked and don't necessarily look completey trashed. I don't really want to spring for new rubbers or go for the cost of the new urathane mounts/pads but would consider it.

I'd like some opinions from guys who have been through this. If the rubbers are crushed is it possible to clean up the whole mount assemblys and perhaps shim em with big washers under?