Wallstreet and Lombard both have 66MHz system busses and can use PC66 SO-DIMMs. If someone went the cheap route on the Wallstreet and only used bare-minimum spec PC66 SDRAM (yes, Apple says you need PC100, but you really only need PC66 - the RAM operates at 66MHz), it may not work in the Pismo which really does require PC100. That seems like a plausible hypothesis for one of your problems to me. It's worth checking the specs on the RAM to learn what it is...

Peace,

Drew