Can anyone help with a couple of nagging problems I'm having with my '68 c-50.

1. The brakes build pressure until they are locking up (and sometimes release pressure and everything is fine and sometimes I have to pull the master cylinder off to release the pressure). I've replaced the booster, master cylinder, brake lines and fluid.

2. The previous owner cobbled a Chrysler Lebaron air cleaner on. I've looked unsuccessfully on ebay and local junk yards for the correct one. What are my options here? Can I find an aftermarket at say NAPA? Will I get more power by getting a larger one?

Thanks.