I feel almost scared to reply to you, with F1 around but:
TE71 has an I-4 setup with lots of room either side so a V6 (2 inline 3 cyls) would easily fit. It's possible that a V8 (2 inline 4's ) would also fit with a bit of relocation & massaging.
Personal choice is the V6 but i'd have to check for sump/road clearnace. if it was an issue he could go for dry sump lubrication, i'm sure it'll clear the hood from the top.
As for the reasoning behind a V6 instead of a High torque V8,... Iforce V8 is a heavy mother! he'd get better torque (and less weight) by going forced induction in the V6. Cheapest solution would be a cobbled (small) turbo & intercooler setup running low boost so as not to have to risk damaging the internals whilst still getting power from lower down in the rev range (it shoudl spool up around 1500 rpm if he want's a great laugh & easy drivability (he wouldn't want a monster kicking in boost at 4000 rpm in a turn....LOL)