Acceleration and other questions on a 90 XJ w. the 4.0

to start, a friend of mine is selling me his 1990 dirt cheap. my 91 needs major engine work(think i might have cracked the block somehow)brakes and tons of body work as well. on the 90 my friend has put new rocker panels on in place of the rusty ones, and just about took care of all the other rust spots. he also had just about the entire brake system replaced(was driving it home on the day of purchase and right outside VIP, the front calipers froze right up. fortunately, he did not have to have it towed because of where it happened. he ended up replacing the calipers, pads, rotors, basically everything)he also replaced the front and rear springs, all 4 shocks, and new bushings as well. i haven't actually looked at the engine yet, but he says you have to put your foot all the way on the gas to go anywhere at all. it starts no prob. i asked when he last did a tune up and he said he hadn't since he bought it. he just changed the oil. before i go and have compression tests and everyuthing, i was going to try something. i just recently did a tuneup on my 91, and was curious what the differences were between the standard 4.0 and the 4.0HO. mainly i'm referring to sparkplug type/gaps. will the HO plugs gappedthe way they are now work in a 4.0, along with the cap and rotor and wires? or do i have to get ones for the 4.0? if not mine have only been used for about 2k miles on the 91. any ideas anyone?

The cap, rotor, plug wires, and plugs are the same so you can swap them all over. If the cat is plugged, performance will be very poor so you might wanna check that out (maybe gut it altogether). If the injectors are still the same factory originals, you might wanna change them for a set of Ford 19lb'ers (orange top). They're cheap and plentiful on e-bay.

Dr. Dyno is correct, a plugged catalytic converter will seriously degrade performance (as well as run hot, creating a fire hazard).

However, he lives in a country that may not require catalytic converters. They are required here and it's a violation of Federal law to remove ar tamper with them. For the record, does not recommend or advocate eliminating or illegally altering any required equipment.

Also, eliminating the cat usually doesn't help performance. You can buy a universal fit cat for $50 or $60, so IMHO it doesn't make sense not to stay legal and keep the air clean.

thanks guys for the tips. as soon as its in the yard, i'll transfer the plugs,cap,wires, and rotor from my 91 on, and then i'll check on the cat. thanks again!