We are looking for a replacement for a blown ls1, we have another 200k mile ls1 but itll take a while to rebuild. Thinking of going 5.3 instead, found one local 04 with 4k miles on it for 700.

What all would need upgraded to get close to ls1 numbers? Already have full exhaust for it ARH 1 7/8 and a catback. ls6 intake, tb, rails, injectors. Have all the accessories and a UD. I know we need to drill for alternator.

Leave cam or swap to ls1?
I know the 241's wouldnt be worth swapping over, comp would drop. How about 243/799 heads?

 

A 5.3 makes a great replacement motor. If just need to get ur car on the road.
all the ls1 parts swap over, prolly gonna have cam and spray to get it to run like the ls1 before

 

With the headers and Ls6 intake the 5.3 will put down about 315 at the wheels. The Ls1 cam and the 5.3 cam are the same up to the 2004 model year IIRC. An Ls6 cam and springs would make it a fun little motor and probably get you 335 at the tires. I don't remember what size the 5.3 combustion chambers are so I don't know if you would lose compression with 243s or not but they would flow better.