I think they're well built engines, at 300hrs we pulled ours down to add roller cams, pistons and heads.
Other than valve springs, they would have gone for several hundred more hrs,they are on snooze. Low compression ,low boost, small cams etc.
The down side is the 420 blowers, it's hard to find parts, I broke two input shafts in the last 3 seasons, which may me partially do to the 7lbs of boost were now running, stock you will see 4lbs or so..
The only down side I see is how very very thirsty these engines are with the pair of 700cfm Holley's per engine.