So my cousin had some guy rebuild his '88 5.0L and now it running extremely rough backfires and cats are glowing red. Where should I start to diagnosis this problem?

 

check the firing order

 

Firing order is correct timing is correct and cats were hollowed out as an attempt so check if they were clogged they no longer glow but car still runs like crap very rough and backfires thru intake

 

what cam was used? roller cam?? flat tappet?? and what firing order are you using, details on the rebuild and parts used??

 

it's bored 10 over, flat racing pistons, rv cam, machined heads, polished crank, and spin balanced engine i'm trying to get more info from him but i'm living in another state at the moment and cant look at the car myself until july :/