Engine damage 99 Cadillac Seville STS

Moin people, I probably did something wrong with my treasure. After the conversion to LPG it took about 5000km and swops, valves burned. Cylinder 1 and 3 0 compression. Despite always meaningful driving on LPG. He never gets more than 3000u/min on LPG with me. My questions now: 1. Is this engine (46 N* 305hp) not suitable for operation with LPG? 2. Let the engine overtake, or rather new unit? (I am thinking of stronger valves/valve seats while overtaking) 3. Then flash-lube in and everything will be fine? 4. Gasumbauer knock over (pictured) because he explicitly told me: Och, Flash-lube do you need net? I thank you already for your answers… Does really hurt to see this eagle stand as a wing-lame duck in the garage. Gruss Marco