They are a drop in replacement.
The exhaust and mounts are the only issues. Factory exhaust (cast iron) rarely fits in the normal way but I think they fit back to front ie with the outlet forward, which makes for great twin turbo opportunities!!! Pacemaker makes off the shelf engine mounts that engineers like. All else is OK. Trans mounts etc (use short case C6) are not changed, just moved to last hole rearwards.
I wish I could have used dual fuel in one way, but then I could not have really got right into the LPG.
It is a work in progress.. as they all are.... I am looking at adding a custom version of a 150 shot nitrous system.
The existing IMPCO convertors can deliver enough gas via their priming circuit to add up to 200hp for 30secs or so. Thats additional HP on top of basic HP.
I havent started buying bits yet, but the theory seems OK.
I cant legally TC/SC the motor without redoing some engineering, but TC is one way I would love to try out.
I guy in the states did a "junkyard" TT EFI 460 for about 3k US.
The site is a bit old now and some links dont work but its real interesting.
You will love a BB. Very lazy power.