opinions on motor situation

[BIGBLU 72]

Here is my situation. The 400 in my 72 GMC has broke one or more oil rings. From my understanding i can drive this motor for a while but it will get worse. so long story short i need to to rebuild or swap.my options are
1.pull the motor and rebuild it!
2. My uncle has an LS3 BBC (complete motor) with 40k original miles that ran great when we pulled it he told me i can have. so i was thinking swap the 400 from my 68 LWB into the Jimmy and freshen up the BBC and drop it in the 68. Selling the 400 in the Jimmy to fund the swap (plus some goodies for the BBC)

Rebuilding the 400 in the 68 was my winter project to get around 350hp and 410 ftlbs. I think that i could get that out of the BBC cheaper without sacraficing too much MPG as the 68 only gets 9 now.

What yall think would be my best route?