From 55 to 57 GM built hydraulic and Solid cam engines. The engine shop is correct in that you need the oil galley holes. There will be holes drilled the lifter bores if it is a haydaulic block. The rule of thumb is that most Powerglide equipped cars from the era were drilled for hydraulics and trucks were mechanical lifters. There is always exceptions to the rule though. The only way is to check for the holes. The early hydraulic motors didn't hold up well anyhow, if you had a 58-62 block, I would say go for it. My advise is to make the engine shop eat the hydraulic valve train and get you the correct mechanical cam and lifters. You're better safe than sorry.
