If its a serious puller, you should have no problem taking a sledge to the firewall when the engine's out either
for the serious pullers that still run a valley charger we build a two piece 4" that routes around like a twin turbo hotpipe would, then goes down like a twin turbo downpipe. then you can run symmetrical 2" or 2 1/4" up pipes. you can only fit so much between firewall and heads..
If its a serious puller, you should have no problem taking a sledge to the firewall when the engine's out either